The topic of my project is a particular application of DNA testing, the testing not of a single suspect suspected for other reasons, but of a very large group, thousands or more, any one of whom might have committed the crime, but none of whom have incurred any particular suspicion. Such a mass testing is known as a "blooding", a term arising from the first case in which this technique was tried, in England in the mid-80's. I had originally planned to discuss only this one English case; however, in the course of my researches, I have encountered enough other examples, that I no longer feel I am discussing a single unique case, but a more and more common method.

A blooding can be implemented when a sample of the perpetrator's DNA is available, for instance, through semen deposited in a rape victim, but almost nothing else is; there are no or few eyewitnesses, for instance. A geographic area, say, a town (though in one case, the blooding of an entire occupational group, truckers, was contemplated but not implemented), is defined, as is a profile, usually males between their teens and their 30's. All persons in the area fitting the profile are then asked to submit blood and/or saliva samples so that their DNA can be compared to the evidence DNA. In most cases, of course, basically all but one if even that, this results in the elimination of the donor as a possible suspect, and in fact, members of the suspect class are invited and encouraged to participate in order to "clear their names", avoid any suspicion whatsoever. Though participation is always voluntary, there is strong social pressure to participate, as well as pressure from the police, and those who for whatever reason decline to do so come under police suspicion, allowing the police to narrow their search and look more closely at a few suspects.

Some of the problems with this method will be obvious at first. There is the civil liberties issue, of unreasonable search, and whether other information is being gathered from the donated samples, and what is being done with it. As a result, this method has never been used in the US, except in the armed forces, but only in Europe. Another problem is the cost; each test can cost in the neighborhood of $75, and this adds up quickly. Another problem is that there is no guarantee that the method will work, testing as it does only a limited group. In an age of quick transportation, perpetrators can slip easily into a town and out, and the police would have no idea where to find them and blood them.

I chose this case and method in a large part because it helped illustrate what for me is one of the most interesting aspects of forensic science, which is the difference between methods which are used to prove the guilt of an arrested suspect in court ("forensic"), and those which are used to find that suspect in the first place ("investigative".) Bloodings are an attempt to use what has become an excellent and standard forensic tool, DNA testing, comparing evidence DNA to that of a suspect, as an investigative tool. As we shall see, it has had mixed results.

The story of the first "blooding", as narrated by Joseph Wambaugh in his book "The Blooding", began in Narborough, a small town near Leicester in central England. On 21 November 1983, a teenaged girl named Lynda Mann was raped and strangled. Her stepfather, who was considered a suspect just because he was her stepfather, was questioned. However, a blood enzyme test, PGM (Phosphoglucomutase), using the semen found on the victim for comparison, quickly eliminated him as a suspect. The PGM type of the perpetrator would be shared by only ten percent of the population, the police were told, but this was not much to go on. Nevertheless, they began testing local men with a record of sex offenses, as well as those associated with a mental hospital near which the crime occurred, 150 men in all. No matches were found. They also decided that due to the high sperm count in the semen sample, the perpetrator had to be young, between 13 and 34, it was somewhat arbitrarily decided. But the police meanwhile relied mainly on "old fashioned detective work", following up every possible lead, every report of someone who might have been near the scene, or who seemed strangely affected or unaffected by the murder. None of the leads led anywhere, but the investigation went on more than a year.

Meanwhile, by an odd coincidence, just a few miles away at Leicester University, Dr. Alec Jeffreys was discovering DNA "fingerprinting" -- RFLP. He published his results in March 1985. Very soon it was being used in paternity testing, including for immigration cases.

In October 1985, there was another attack on a young woman in the Narborough area. And on 31 July 1986, in the neighboring town of Enderby, another teenaged girl, Dawn Ashcroft, was raped and murdered. Although there was no conclusive link between the crimes other than the modus operandi, the police used the same methods to investigate, asking everyone, following every lead. Eventually, one of these leads led somewhere. A young man who worked at the hospital and had a history of molesting children, whose motorbike had been glimpsed near the scene of the Ashcroft murder, was arrested. As perhaps happens more frequently in Britain than this country, he began to confess, wildly, telling all sort of stories that frequently contradicted each other. Still, the police were sure they had the right man. According to Wambaugh, it is not certain who first pressed for the use of the new DNA testing method, the police, to confirm guilt, or the family of the accused, in the hope of exculpating him. But Jeffreys was given his first chance to apply his method to a criminal case. What he concluded was that the two rape/murders, of Lynda Mann and Dawn Ashcroft, were committed by the same person -- but not by the suspect in custody. This was the first case of a suspect freed because of DNA testing. But this did not help find the real rapist/killer.

It was at this point that the police decided on the blooding. Males between the ages of 16 and 34 were asked to come to a station to donate blood and saliva. No one was forced to give a sample, but the police would strongly encourage, even cajole, people into doing so, or at least make it as convenient as possible to donate, making house calls when the man could not or would not make it to the testing station. Response was 98%; people seemed genuinely outraged by the crime and to want to do whatever they could to help solve it. Still, a few people avoided the test, skipping town. Presumably, they had other things to hide.

The samples were first given the PGM test, and only those that passed that were tested for a DNA match. But by May of 1987, 3653 men had been tested, and 2000 eliminated from suspicion. (In all, 4653 were tested.) There was a long backlog at the laboratory, which was not prepared for industrial scale testing of this type. And as the testing went on and no suspect was found, the testing was widened, so that men who had first been excluded because they had alibis were now tested anyway. This of course helped raise the cost, which was about thirty pounds per test.

Critics of bloodings have always said that the guilty party would simply decline to come in for testing. Supporters respond that is what would identify him. And in the end, this is what happened. The actual killer, Colin Pitchfork, a baker with a wife and child, and also history of flashing and extramarital affairs, became scared. He had not been closely questioned during the initial search of sex offenders because of the relatively mild nature of his offense. He had no fingerprints on file. There had been nothing to link him to the crime before and he had not even lived in Narborough at the time of the first murder, but in a neighboring town. When he knew of the blooding, he desperately tried to find someone else to take the test for him, offering money to co-workers, claiming that he was terrified of the police because of his past, or that he had already taken the test for someone else who was so terrified. He finally found a dupe, and with a faked ID card, pulled it off. However, he had not reckoned on his substitutes loose tongue after a few beers. The substitute casually mentioned the deception in a bar, and the information was heard and relayed to the police, who quickly went to question the Pitchfork, who confessed immediately. He pleaded guilty to the crimes and thus no evidence, DNA or otherwise, was ever introduced. However, the PGM and the DNA tests were performed and did match.

Since then, there have been several other cases in which mass testing has been tried in criminal cases, with varying results. In 1990 in South Wales, 5000 men were tested in a rape/murder case, with no results. However, in 1995 Claire Denise Hood was raped and murdered in Cardiff, Wales. When other methods failed, 2000 men, as young as 13, from the neighborhood of St. Mellon's were blooded, at a cost of about $150,000. At one house, police had gone only to blood one man, when the mother reminded them that she had two other sons they were welcome to check. What she did not know was that one of them, Neil Owen, 19, was the murderer. He took the test, and when the police came back to ask him why the semen on the victim appeared to be his, told an elaborate story of having had an affair with the girl, but denied killing her. The jury did not believe him, and he was convicted, this marking the only time anyone has been convicted of a crime through DNA evidence through a blooding.

In December 1995, a French student named Celine Figard was found raped and murdered in southern England. Because she had last been seen accepting a ride in a white Mercedes truck, a plan was floated to "blood" all 1200 drivers of such trucks in England. (Another source gave a figure of 7500 -- perhaps this was before the type of truck had been specified.) However, this proved not to be necessary; a truck driver was identified by other evidence, including having shaved his beard to confound descriptions, and having had the woman's belongings in his possession. I could not confirm if his DNA was ever tested; however, DNA testing was used to confirm that the drops of blood found on the seat of the truck were Celine Figard's.

There are currently two cases involving bloodings going on. Caroline Dickinson, 13 year old English girl, was raped and smothered in a youth hostel in Pleine-Fougeres, in northern France, in July 1996. A suspect was soon arrested and confessed, but DNA testing, as in Narborough, showed he could not be the culprit. Schoolmates on the trip with the victim were tested first, but with no result. Although a composite picture and description of the killer has been assembled, the investigation seemed to have hit an impasse, the girl's father, John, pushed for a blooding, and when the judge in the case resisted, managed to get him replaced. One hundred sixty nine men out of the village of 1800, those between the ages of 15 and 35, were tested in late 1997, and when they were all negative, an additional 252, aged 35 to 60, were also tested, again with no results. Since the killing of Caroline Dickinson has been linked to a crime in another town by the presence of a piece of cloth from the other victim's room at the Dickinson crime scene, it seems very likely that the killer came from outside Pleine-Fougeres and thus would not have been caught in the blooding. There is talk of extending the blooding to other towns.

In Cloppenberg in northwestern Germany, Christina Nytch was raped and strangled on her way to school last year. As in the Dickinson case, the crime has been linked to others, and a composite picture circulated. However, 18000 men, all those in the Cloppenberg area between 18 and 30, are to be tested. This will be the largest blooding ever. .

As these cases show, bloodings can be a potent investigatory tool. In one case, a blooding identified the criminal directly, in another, a blooding flushed him out. In other words, bloodings can work just because people think they work. But bloodings are very inefficient. Even if the target class of individuals to be tested can be narrowed somewhat by other evidence, a vast amount of work must be organized and done, a vast amount of information kept track of, a great cost incurred. This is why bloodings tend to be done in emotionally laden cases, rapes and murders of young women, when the police must convince relatives, the public, and themselves that they are doing everything they possibly can. (Although it must also be said that DNA information on the perpetrator is rarely so readily available as in a rape case.) A blooding is dramatic, and it is good public relations.

Also, bloodings are not very reliable. Ease of transportation means that a killer could have come from anywhere, not just a small town, though often rapists of children are not strangers but do come from the area. (As in the Hood case.) If a whole town is blooded and there are no positives, that does not prove very much. It is like the joke about the man looking for his keys under the streetlamp even though he lost them across the street, because that is where the light is better. It is a lot easier to test a whole town than a whole country.

Another problem is that the more tests that are done, the greater the chance of a mistake. Since most results are going to be negative, this means a false negative. In other words, the culprit's DNA could test negative, and no one would have any reason to retest it. In a case in which there is an obvious suspect, such as the O.J. Simpson case, if the test is negative, you might have good reason to do it again. But there is no reason to retest thousands of samples, when you have no particular reason to believe that any one of them really is the culprit.

Then, of course, there are the civil liberties issues. I doubt that a blooding would ever be permitted in the U.S. There would be too much distrust and uncertainty over the fate of the samples, and more important, of the information gained. In previous bloodings, police have promised to destroy both samples and information at the end of the investigation. However, those same police agencies have also talked of building databases of the DNA fingerprints not just of convicted criminals but of criminal suspects. Supposedly, participation is always voluntary, but all involved seem to accept that anyone who declined to participate would be inviting suspicion on himself and deservedly so. On the other hand, if a large number of people declined to participate, it would invalidate the blooding.

The theoretical (even philosophical) aspect of bloodings cases has to do with the very nature of questions and what questions forensic science is supposed to answer. In class we have learned that forensic science deals with yes-no questions (even if they can only be answered probabilistically, not actually yes or no.) Does the evidence sample match the suspect sample? Can we put the suspect at the scene of the crime? Ultimately leading up to the question, "Did the suspect commit the crime?" Because under our system, as opposed, say, to that of certain European countries, the court does not strive to find the facts, only to determine if the "facts" presented to it are true or not (are actually facts.)

This is a very different process from the investigatory process, in which so-called "wh-questions" (the term is from linguistics) are asked. Who did it? how? why? These questions are quite open-ended. They do not involve the comparison of two things which either match or don't (or have a probability of matching or don't.) Rather they involve the search for a thing which may or may not be there.

Now, "wh-questions" can be answered one of two ways. Rarely, they can be posed directly to witnesses, though this is what "traditional detective work" relies on. (It was not very effective in the Narborough murders.) "Whom did you see running away?" is a wh-question. But most of the time, wh-questions must be reduced to a longer or shorter series of yes-no questions. (As if one is talking to a source like Deep Throat who, to assuage his conscience, will confirm or deny but not provide information.) A witness may not be able to identify or describe a suspect, but he or she can pick him or here out of a lineup, at which the question is "Is it this one? Is it that one?" In other words, confirmatory procedures, which are what forensic, court-oriented sciene is all about, can be used as exploratory ones.

The problem is that in many investigations, the pool of even potential suspects is so large, because the other evidence by which the pool could be narrowed is so limited, that it is not possible to ask the yes-no questions, not possible to bring everyone to a lineup. Interestingly, these are often cases in which once a suspect is caught, enough evidence is found, or the available evidence can now be used in yes-no questions, to convict easily. An example is the Unabom case, in which the perpetrator, it seemed, could be almost anyone in the U.S. The FBI had tantalizing clues but no way to follow them up using investigatory methods. They had no suspects with whom to make comparisons. Once a suspect had been identified, however, it was very easy to ask the right yes-no questions, and the ample evidence in the cabin confirmed the identification.

Fingerprint identification works by looking for matches in a large but finite database. If there is no match in the database, this does not mean that no match exist, just that the database cannot answer the question. It is like when a match cannot be confirmed due to the limitations on the accuracy of a testing method.

Even the few wh-questions that are asked in forensics, such as "what is this white powder?" or "what is this ignitable fluid?" either come down to yes-no questions because there is only one thing that really matters ("is it cocaine? because if it is not, it does not matter..) or because the only way to identify a substance is by comparing its characteristics (appearance, spectrogram, etc.) to those of known substances in a series of yes-no questions. Is it cocaine? Is it pseudoallococaine? until there is a match.

In other words, in order to answer most, theoretically all, wh-questions, in an investigation, they must be reduced, broken down, to a finite number of forensic type yes-no comparison questions. (Finite in the sense that the questioning must be restricted to a certain number of possible suspects, or the search goes on forever.)

DNA testing is very good at answering the yes-no question of whether a suspect was present at the scene of a crime. But that suspect must be known, or rather, suspected. DNA testing cannot, like luminol, make the guilty party stand out from the general population. He must be asked for a sample for comparison, so that a yes-no question can be asked. If there is no suspect, then a blooding is the only possibility. By treating everyone as a sample, by asking the yes-no question of everyone, one hopes that someone will finally answer yes. Again, the yes-no question style of forensic science has been translated to meet the wh-question needs of investigation.

Solving questions this way is something like trying to translate from German with only an English-German dictionary. To look up a word, one must read through the whole dictionary. It is like the solution to the four-color map theorem in mathematics, which proved that any map can be colored with four colors, with no two adjacent areas having the same color, by reducing all possible map patterns to a finite number of cases and proving each one individually by a computer program, for a 300,000 page proof. It was called inelegant and "brute-force" but it worked. It is also like checking algebra problems by plugging answer back into the equation. It can be hard to get the answer -- this is a wh-question. But once one has an answer, it is very easy to test. However, if the "answer" fails, then in theory one would have to try every possible number back in the equation until one found one that worked, hardly a pleasant prospect. However, it could be rendered more doable if the field of possibilities could somehow be limited, to positive integers, whole numbers, etc. This is of course what is tried in bloodings cases. The huge time and effort requred can be reduced substantially through the exclusion of whole classes of people based on other evidence. In these cases, it is vital that the exclusion be made for valid reasons; otherwise, the wrong (or rather the right) people will be excluded and never asked the all-important yes-no question.

Lastly, forensic techniques have another important investigatory use, though a controversial one. They can be used to play on a suspect's fear of being caught, even if they might not actually work and could not be used. In the Narborough case, the DNA testing was only used to confirm that the test actually worked. It was not even brought up at trial, because there was no trial; the suspect had confessed, sure he would be convicted anyway. And he only gave himself away because avoided the test, fearing it would give him away. In other words, the test's reputation, not the test itself, caught the killer. The test might well have been a complete bluff. It might have been as if a detective had a hunch, a gut feeling, which he knew would never stand up in court, but confronted the suspect with it in such a way that the suspect was sure he would be convicted and talked, whereas a smarter suspect, knowing more about the limitations of forensic science (and of the police and prosecutors to use it) might have kept his head, refused to answer questions, and gotten away just because the police, despite their certainty, would not have had any evidence for the court. Of course, their suspicions might have led them to watch the suspect more carefully and thus get something hard on him. So another way to answer a wh-question is to see who does not want to answer the yes-no question.

I think, despite some spectacular successes and interesting failures, bloodings will have only a limited usefulness for criminal investigation and prosecution in the foreseeable future. However, as more and more information is available and easily checkable on computers, and computers come to be able to check it more quickly, and the costs in time, money, and effort of individual comparison tests are reduced, and as fear of crime continues to erode civil liberties protection, mass applications of forensic comparison methods to investigations will probably rise.