A little puzzle for you to solve (taken from a true crime):
A female patient charged her doctor with sexual assault. Semen swabs were collected from her clothing. The doctor voluntarily provided blood samples for DNA testing a total of three times. The DNA from his blood did not match the DNA from the swabs. The samples were not tampered with because his blood was taken each time by a certified nurse, in the presence of police, even videotaped, and sent to the forensic science labs under their supervision.
The fourth time, the police had a warrant. They collected blood samples from his finger, NOT from his arm as he had demanded in the previous three cases. The DNA matched! He was found guilty and sentenced to 6 years.
Question: How did he manage to fool everyone the first three times? Why did the blood taken from his arm did not match the swabs but the blood taken from his finger did?
…people can’t be aware of nitty gritty of forensic science…
The solution has nothing to do with forensic science. Philosophy is quite close.