A prisoner already serving 16 life sentences killed three fellow inmates in a single day at Arizona State Prison near Tucson on April 4. All three victims had been convicted of sex crimes against children.

Ricky Wassenaar first strangled his cellmate Saul Alvarez inside their shared cell. He then went onto the prison yard armed with a large rock inside a fishnet laundry bag, killing Thorne Harnage and Donald Lashley as they waited to enter the breakfast hall.

After the killings, Wassenaar called the Arizona Mirror and reportedly said he had no regrets, adding: “The taxpayers no longer have to pay for them. I’m paying my debt to society.”

Wassenaar was already serving life sentences for a 2004 prison standoff in which he and another inmate held two guards hostage for 15 days, one of the longest such events in U.S. history.

He has now been charged with three counts of first-degree murder and pleaded not guilty, despite publicly confessing to the attacks. Prosecutors are reportedly considering seeking the death penalty.

Authorities are investigating the circumstances of the killings, which have raised questions about prison safety and management of violent inmates.

This incident has shocked both Arizona residents and the nation, highlighting the dangers posed by high-risk prisoners even while incarcerated.