NEW YORK — In a move likely to renew a longstanding ethical controversy, geneticists are making plans to study the DNA of Adam Lanza, 20, who killed 20 children and seven adults in Newtown, Conn. Their work will be an effort to discover biological clues to extreme violence.

The researchers, at the University of Connecticut, confirmed their plans through a spokeswoman but declined to provide details. But other researchers speculated that the geneticists might look for mutations that might be associated with mental illnesses and ones that might also increase the risk for violence.