An American man serving a prison sentence in the Czech Republic committed suicide Thursday, authorities said. Kevin Dahlgren was serving a life sentence for killing four members of his family.

“I can confirm that we had a death by suicide in one of our prisons,” Petra Kucerova, spokeswoman for the Czech Prison Service, told Agence France Presse. “I cannot give you more information as the case is under police investigation. But a prisoner has died.”

Dahlgren, who was from California, was sentenced to life in 2016 after he was convicted of stabbing four of his relatives to death in 2013. The members of his family were Czech and he was in the country visiting them, Reuters reported.

Dahlgren was convicted of murdering his aunt, uncle and two cousins before trying to burn their bodies. Prosecutors said some of them were stabbed up to 29 times.

“He maliciously attacked four members of the family who had been kind to him, who had given him shelter, who had helped him, who had done him no wrong…and murdered all four of them in a very brutal way,” Judge Michal Zamecnik said during sentencing, according to Reuters. “He wiped out a whole family.”

Dahlgren attempted to flee to the United States after the murders but was arrested upon arrival at Washington Dulles International Airport and extradited to the Czech Republic. Dahlgren did not testify during the trial, though defense attorneys said he was mentally ill.

“I had no control [over] any of my actions,” he reportedly told the judge, according to UPI. “I could only do what the voice instructed me to do. What happened to the family is a tragedy.”

The judge in the case, however, ruled Dahlgren sane.

After his sentencing, local news outlets reported he planned to file an appeal of the verdict.

“Not only did he commit a crime, but he is also fully responsible for it,” Zamecnik said at the time, according to CBS News.

Dahlgren was behind bars in Valdice prison, one of the toughest-security prisons in the country, when he committed suicide, according to the Prague Daily Monitor. No other details were released regarding his death.

The headline of this story has been updated to reflect that Dahlgren was convicted of quadruple murder, not triple murder.