Forensic science
In 1929 Kirk became professor of biochemistry at UC Berkeley. According to Kirk, he first became interested in forensic science in his early days as a teacher after a student asked if it could be determined if a dog had died of poisoning. Forensic science permanently piqued his interest when authorities asked him to do a microscopic examination of a rape victim's clothing. He found fibers from the attacker's shirt and this evidence resulted in a conviction. In 1937, Kirk became leader of UC Berkeley's criminology program. Due to his extensive experience in microscopy, Kirk was asked to join the Manhattan Project where he worked on the process to isolate fissionable plutonium from 1942 to 1945. When he returned to Berkeley, he created a major in technical criminology and when August Vollmer established the UC School of Criminology, Kirk was appointed to chair the criminalistics department.