An Arizona inmate already serving 16 life sentences for raping and taking guards hostage during a 15-day standoff two decades ago is now accused of murdering three fellow inmates.

It happened Friday morning at the Arizona Department of Corrections, Rehabilitation & Reentry facility in Tucson, the agency said in a press release. The suspect was identified as Ricky Wassenaar, who has been in and out of prison since the 1980s. He’s accused of killing inmates Saul Alvarez, Thorne Harnage and Donald Lashley.

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Officials have yet to say what led up to the slayings, nor have they given a motive other than saying Wassenaar “acted with an intent to harm” the three victims. He has yet to be formally charged. Per the press release, Alvarez was a convicted murderer while Harnage and Lashley were sentenced for sexual conduct with a minor. Lashley also was convicted of molestation of a child.

The agency’s Office of Inspector General will investigate the deaths.

“The ADCRR takes situations involving violence seriously and will pursue prosecution against any suspects believed to be involved in the case,” the press release says.

Saul Alvarez, Thorne Harnage and Donald Lashley (Arizona Department of Corrections).

Wassenaar gained notoriety in 2004 when he led a hostage situation at the Lewis facility. Local CBS affiliate KOLD reported that Wassenaar used a homemade weapon and overpowered a guard in the kitchen before stealing his uniform. He then went to the watchtower with a fellow inmate where he tricked the guard inside to let them inside.

The other inmate struck the male guard in the head and they held him and a female guard hostage. They let the male guard go after six days but held the woman guard for the duration. The guard, Lois Fraley, did an interview with KOLD about a year after the incident.

“I considered myself dead from the beginning,” she said.