On the night of 31 October 1992, Schneeberger sedated his 23-year-old patient, Candice, and raped her. While Versed — the anesthetic he used — has strong amnesiac effect, Candice was still able to remember the rape. She reported the crime to the police.
Scheenburger's blood sample was, however, found not to match the samples of the alleged rapist's semen, thus clearing him of suspicion. In 1993, at the victim's request, the test was repeated, but the result was negative, as well. In 1994, the case was closed.
Candice, still convinced that her reminiscences were true, hired Larry O'Brien, a private detective, to investigate the case. He broke into Schneeberger's car and obtained another DNA sample, which, this time, matched the semen on victim's panties and pants. As a result, third official test was organized. The obtained blood sample was, however, found to be too small and of too poor quality to be useful for analysis.
In 1997, Lisa Schneeberger found out that her husband had repeatedly drugged and raped her 15-year-old daughter from her first marriage. She reported him to the police, which ordered fourth DNA test. This time, multiple samples were taken: blood, mouth swab, and hair follicle. All three matched the rapist's semen.
During his 1999 trial, Schneeberger revealed the method he used to foil the DNA tests. He implanted a 15 cm Penrose drain filled with another man's blood and anticoagulants in his arm. During tests, he tricked the laboratory technician to obtain blood sample from the place the tube was planted.
He was found guilty of sexual assault, of administering a noxious substance, and of obstruction of justice, and received a six-year prison sentence.
(Source: From Wikipedia)
The value of DNA evidence has to be seen in light of recent cases where criminals planted fake DNA samples at crime scenes. In the case above, Dr John Schneeberger planted fake DNA evidence in his own body: Dr. Schneeberger raped his sedated patients and left semen on her underwear. Police drew Schneeberger's blood and compared its DNA against the crime scene semen DNA on three occasions, never showing a match. It turned out that he had surgically inserted a Penrose drain into his arm and filled it with foreign blood and anticoagulants.
A Penrose drain is a surgical device placed in a wound to drain fluid. It consists of a soft rubber tube placed in a wound area to prevent the build up of fluid.
A Penrose drain removes fluid from a wound area. Frequently it is put in place by a surgeon after a procedure is complete to prevent the area from accumulating fluid, such as blood, which could serve as a medium for bacteria to grow in.
An anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders.
Anticoagulants are given to people to stop thrombosis (blood clotting inappropriately in the blood vessels).
Read more about DNA: Genetic fingerprinting at Wikipedia: DNA Test