The physical evidence in the case consisted of a visible drainage stain on the complainant’s underwear. This stain was tested and shown to contain semen, and ABO typing showed that it had B and H group substances. The suspect was thus included as a possible source of the semen. After a trial at which Crowell-Webb testified that he was her attacker, Dotson was convicted of sexual assault and sent to prison. The conviction was based on Crowell’s testimony, but also on the testimony of a forensic scientist about the physical evidence just described.
Six years later Crowell, by then married and called Crowell-Webb, announced at a press conference that she had lied about Dotson’s involvement: She had not been sexually assaulted at all, and the semen in evidence belonged to a consensual partner. This action caused a major furor in the press and in the courts. Eventually DNA typing proved that the semen in evidence was in fact not from Dotson but from another man who was Crowell-Webb’s boyfriend at the time of the alleged assault. Dotson was released from prison. Cathleen Crowell-Webb died in May 2008 at the age of 46.
In the scrutiny the case received after Crowell-Webb recanted her trial testimony, it came out that the forensic biologist who had done the original analysis had misinterpreted his findings. He had said that only a B secretor male could be the source of the semen. That is not true, as the following table shows.
The table shows that a male who is a B secretor could be the source of the semen found in the underwear, as the analyst said. But the source could also be a type O secretor or a nonsecretor of any ABO type. Semen from males of any of the three combinations mixed with the secretions of a B secretor female would yield the same results upon typing the mixture.
The reason this point matters is because the expert usually gives the court a percentage of the population who could be sources. Type B secretors are about 7 percent of the Caucasian population and 15 percent of the African-American population. (It is general practice to state the population percentages for different racial groups, because the blood type frequencies are different among the groups.)
But given that the source could also have been an O secretor or a nonsecretor, the sum of those three groups represents about 66 percent of the Caucasian and 85 percent of the African-American populations. Even understanding that 7 percent or 15 percent of the population is a lot of people, there is quite a difference between telling the jury that the defendant is in a population group of potential semen sources that is 7 or 15 percent versus one that is 66 or 85 percent.
This is an example of an inclusion case, the defendant was included as a potential source of the semen found in the evidence. It demonstrates two things: First, including the person as a possible source of the semen stain does not mean he is the source and, second, accurately presenting the findings to the court is important. Telling the court that only 7 percent of Caucasian or 15 percent of African-American males could have been sources was simply wrong and could well have misled the jury.
