One frequent claim I get from anonymous commenters is that if no sperm is detected when a rape kit is processed that this is proof that no sexual assault occurred.
This claim is false.
Sperm and seminal fluid are not always present in sexual assault cases, but that does not mean the crime did not take place.7,11 Several explanations for the absence of detectable semen in sexual assault are a lack of sexual contact; sexual contact without ejaculation; and sexual contact with loss of semen between the time of contact and collection of evidence.9
Studies have shown that 34 percent or more of rapists are sexually dysfunctional, and as many as 40 percent wear condoms.7
To illustrate that the lack of useful DNA evidence does not prove the defendant's innocence, I'll highlight sections from Commonwealth (Massachusetts) vs. Roland Walker.
In November, 1998, after a fourteen-day jury trial in the Superior Court, the defendant was convicted on eleven indictments alleging manslaughter, assault with intent to rape, drugging a person for sexual intercourse, four counts of assault and battery by means of a dangerous weapon, and four counts of mingling poison with food, drink, or medicine. The defendant was acquitted of one count of rape. The indictments concerned three incidents in which the defendant entertained female guests in his home and served them beverages that also contained a sleeping medication. After drinking the concoction each woman lost consciousness and, in one case, died. In another instance the unconscious victim was sexually assaulted. [...]
A blood screen was done at the hospital and benzodiazepine was discovered in blood samples from both women. [...] Rape kits were also prepared at the hospital. E.R.'s rape kit yielded nothing of evidentiary significance, while D.K.'s rape kit revealed the presence of seminal fluid and sperm cells on her underpants. DNA testing could not exclude the defendant as a possible contributor to the genetic material found on the underpants, and statistical analysis showed that about twelve percent of African-Americans could have contributed to the stain on the underpants. The defendant is African-American. [...]
Rule 9(a)(1) of the Massachusetts Rules of Criminal Procedure, 378 Mass. 859 (1979), allows joinder if the offenses are based on "a course of criminal conduct or series of criminal episodes connected together or constituting parts of a single scheme or plan." The facts of this case demonstrate a series of criminal episodes that are sufficiently connected together to support the allowance of the request for joinder. In each episode, the defendant brought women to his home, drugged them with a drink containing a sleeping medication, and then engaged in conduct that could be construed as a sexual assault or an attempted sexual assault.
The evidence against this defendant was strong enough to make it clear that sexual assault was directed at the 4 victims included in this case despite the lack of DNA evidence being detected on any of the surviving victims' bodies.
DNA was found on the deceased victim's body, but the defendant claimed the sex was consensual. However, the medical expert testified that this woman was given four to six times the therapeutic dose of temazepam, a sleeping medicine, and that drug was mixed with alcohol -- something the defendant's prescription specifically warned against.
DNA evidence was only found on the body of the 4th victim, but that woman's unresponsiveness may have interrupted the defendant's pattern of cleaning up his victims' bodies before the women regained consciousness.
The only charges which were overturned were those related to the poisoning of the 3 surviving victims since the test results didn't record the amount of drugs found. They had been drugged, but there wasn't enough evidence to prove that they had been poisoned.
If the final victim hadn't died from a mix of alcohol and sleeping medicine, this man might not have been tried for his crimes against the 3 previous surviving victims. Without that 4th case, where a woman died, some people who knew he was a suspect might wrongly claim that it had been proven that he had been falsely accused.
Certainly, a 71-year-old retiree who committed his crimes in his own home doesn't fit most people's stereotypes about real sex criminals.
Those who are among the quickest to wrongfully accuse women of having filed false police reports claim to be against wrongful accusations. No wonder so many of these people choose to remain anonymous.
This case also highlights why so many people who put forth incorrect information demand that rape victims have proof of their rapes before they report their rapes to the police. Without those prior crimes, the jury might have believed that there was reasonable doubt about whether the deceased woman had voluntarily mixed sleeping medicine with alcohol.