The Stillwater prison inmate accused of killing a corrections officer had a "significant" discipline record but eventually had earned a spot working in the prison's industrial building, Minnesota Department of Corrections officials said Thursday.

And it was there where he allegedly killed officer Joseph Gomm on Wednesday afternoon.

The prison remained locked down Thursday out of an "abundance of caution," DOC Commissioner Tom Roy said at a news conference. The situation is being assessed daily, but so far prison officials haven't seen any "accelerated behaviors," he said.

After the attack, Edward Muhammad Johnson, 42, the inmate accused of killing Gomm, was moved to the more restrictive maximum-security prison in Oak Park Heights.

Johnson has a long history of violence. He is serving a 29-year term for fatally stabbing his 22-year-old roommate, Brooke Thompson, while her 5-year-old daughter was nearby in their Bloomington home in 2002.

Late that year, while in the Hennepin County jail during his trial, Johnson assaulted a deputy, authorities say. He ignored orders to stay out of a certain area of the jail and punched the deputy in the eye, leaving him with a cut, according to the charges. He pleaded guilty to fourth-degree assault and was given a 10-month term.

A few months later, Johnson pleaded guilty to killing Thompson. In March 2003, he began serving his time at Stillwater for that crime.

Since then, Johnson has racked up 1,695 days in segregation for numerous offenses, including 540 days in connection with a prison fight in July 2004, authorities said. During that fight, he was stabbed in the right eye by a fellow inmate with whom he'd had a long-running dispute. The attack cost Johnson his eye.

Johnson sued the head of the DOC and a number of corrections officers at the time and won a $500,000 jury verdict in state court, but the law capped that amount at $300,000. His attorney in that case, Jordan Kushner, said Gomm's name never came up in connection with that case.

Johnson's financial award inspired a wrongful-death suit filed by the family of the woman he killed. In 2010, her immediate survivors received $160,000, most of the money Johnson had won from the state, Kushner said.

Johnson was most recently sentenced to segregation in June 2016. Since then, he had demonstrated "relatively good behavior" and had been allowed to work in the prison industrial building, Roy said.

"Those are valued positions," he said. "As an agency, we encourage vocational training and work."

Inmate assaults on prison officials are a "sad reality" faced by those working in prisons and county jails, Roy said.

Roy and Washington County Attorney Pete Orput declined to discuss details of the fatal assault until the investigation is completed. However, sources told the Star Tribune that Gomm was bludgeoned with a hammer and stabbed. According to the Ramsey County medical examiner, he died from blunt-force trauma.

Gomm, 45, of Blaine, is the first corrections officer in Minnesota killed in the line of duty, according to a national organization that monitors law enforcement deaths, the Officer Down Memorial Page. Colleagues said he was hardworking and well-respected.

"I consider those correction officers heroic in what they do, and all I can do in return is bring them the most aggressive prosecution we can muster," Orput said, adding that he will seek the sternest possible punishment for Johnson.

An online fundraiser has been started on gofundme.com to support Gomm's family.

Since taking office in 2011, Orput said, he's prosecuted about 150 inmates for assaults — most of them against corrections officers. And in all those cases, the inmates received consecutive sentences that added on to their time in prison.

Johnson was to have been released from prison in late 2022 and then serve the balance of his sentence on supervised release. However, a conviction for Gomm's death could keep him behind bars for the rest of his life.

A troubled past

Johnson's sister, Zakiyyah Johnson, expressed grief Thursday and apologized for the anguish the officer's family is feeling. "If this was not a case of self-defense, then I'm sorry," she said. "My whole family and I grieve for them."

Johnson and his sister became orphans in 1988 in Chicago after their father, Edward Sr., killed their mother, Selena, and then himself. Both parents were Chicago police officers.

The Johnson siblings are great-grandchildren to Elijah Muhammad, the founder of the Nation of Islam, according to Zakiyyah Johnson. Their mother was one of Muhammad's grandchildren.

Zakiyyah Johnson said she was 8 and Edward was 12 when they moved to the Twin Cities to be raised by an aunt. They went to Bloomington Kennedy High School. While they were both traumatized by their parents' violent deaths, "Edward was brilliant," she said. "I always struggled in school."

She said she saw her brother only once after his roommate's killing. "It was awkward," she recalled. "He killed a woman who was basically the same age as me. I wondered how he could do that with what happened to our parents. He literally had no reason."

Nearly every prison inmate comes with "baggage," said Roy, the DOC commissioner. "There are a large number of offenders who sometimes after decades move along in their lives and have abandoned gang affiliations, no discipline for years and years," he said. "But not everybody subscribes to those kind of changes."