The parents of a gunman who shot and killed a Pennsylvania trooper engaged in “psychological manipulation” of their son and should be held responsible for the deadly ambush at a state police barracks, according to a lawsuit filed by the trooper’s widow.

Eugene Michael and Deborah Frein manipulated their son, Eric Frein, into “developing a strong dislike for police and acting on that dislike,” said the wrongful death suit, filed last week by Tiffany Dickson.

Eric Frein, now 34, was living with his parents in Canadensis when Cpl. Bryon Dickson, a 38-year-old Marine veteran, was fatally shot and Trooper Alex Douglass was permanently disabled in the Sept. 12, 2014 attack at the Blooming Grove barracks. Frein, who eluded capture for 48 days, was convicted in April and received a death sentence.

“We are seeking justice on behalf of the Dickson family for the loss of this courageous husband, father and son,” Tiffany Dickson’s lawyer, Marion Munley, said in a statement Monday. “We stand by the allegations in the complaint and believe that Frein’s parents bear responsibility for what happened to Cpl. Dickson.”

The couple didn’t immediately return a call Monday from The Associated Press.

Dickson’s lawsuit, filed in Lackawanna County Court, seeks monetary damages against Frein’s parents and from Frein himself.

Michael Frein testified at the trial that he shared his political views with his son, telling Eric that “government’s too big” and citing a number of cases in which police had shot and killed suspects as “bad police work.” But he said he never encouraged Eric Frein to target police.

Frein wrote a letter to his parents while on the run in which he advocated revolution to “get us back the liberties we once had.”

Tiffany Dickson’s lawsuit said Michael Frein had exercised “significant influence over Eric,” imparting “dangerous views on government, the power of the police, and the use of firearms.” The suit noted Michael Frein, who had a long career in the military, taught his son how to shoot, and that Eric had easy access to weapons in the house, including the rifle used to shoot Dickson and Douglass.

Douglass and a state police dispatcher have initiated separate lawsuits against Frein’s parents.

There is precedent in Pennsylvania for suing the parents of an adult perpetrator.

Richard Baumhammers, a white, unemployed immigration lawyer who lived with his parents, was convicted and sentenced to death in the 2000 killings of five ethnic minorities in a racially motivated attack outside Pittsburgh. The victims’ families sued Baumhammer’s parents, saying they failed to get mental health treatment for their son, take away his handgun or alert authorities.

The case went to the state Supreme Court. The parents ultimately settled for $785,000.

Under Pennsylvania law, parents can be held liable for damages caused by their minor children. Because Frein was an adult when he killed Dickson, the lawsuit against his parents hinges on whether they were negligent, said Pittsburgh personal injury lawyer Richard Ogrodowski.

Tiffany Dickson’s lawyer has to prove that Frein’s parents “knew this person had the propensity to do that, was going to do that, yet did nothing about it,” he said.