(CNN) -- Geneticists have begun studying the DNA of Connecticut gunman Adam Lanza, a spokeswoman for the University of Connecticut Health Center said Thursday.
The geneticists were asked to join the investigation by the state medical examiner's office, spokeswoman Carolyn Pennington told CNN. She said there is no specific genetic marker the team is looking for, and that lab results and a complete analysis of the DNA "are not expected for several weeks ... probably the end of January."
CNN Chief Medical Correspondent Dr. Sanjay Gupta said it is unlikely investigators will be able to find a genetic clue for what motivated Lanza, who fatally shot 26 people, including 20 children, in the attack on Sandy Hook Elementary School in Newtown, Connecticut on December 14. Lanza, who had also killed his mother before the school massacre, took his own life with a gunshot to the head.
"There's no clear-cut sort of ... genes identified with the types of illnesses, mental illnesses, that may cause this sort of behavior," says Gupta.
Not only that, Gupta said, but "there are people who carry these genes who don't have the behavior still. I think it's very hard to sort of put those two things together."
Experts in genetics agree. Although there are genetic components to many mental illnesses, there are hundreds, perhaps thousands, of genes involved. Most believe that no single gene or mutation could be the smoking gun that foretells violent acts like those committed by Lanza.
"There's nothing you could look at that would give an answer," said Steve Warren, chairman of the Department of Human Genetics at Emory University.
"We don't know a gene that says 'this person has schizophrenia.' There's no way to come up with a conclusion that way."
CNN's Caleb Hellerman contributed to this report.