The man who opened fire at the Molson Coors plant Wednesday, killing five co-workers and himself, had been involved in a long-running dispute with a co-worker that boiled over before he came back with two guns and started shooting, according to law enforcement and brewery sources.

Anthony N. Ferrill, 51, had worked as an electrician for more than 20 years, about 17 of them at Molson Coors, according to multiple sources and online employment records. Police confirmed he was the shooter at a Thursday afternoon news conference.

A co-worker who asked not to be identified for fear of being disciplined said Ferrill believed he was being discriminated against because he was African American, and that he frequently argued with at least one of the victims.

The co-worker said Ferrill often watched movies on his phone during the day, which the other man took issue with, and that the two accused each other of going into each others' offices and stealing tools or tampering with computer equipment.

Law enforcement officials said Thursday that no motive has been determined.

Asked at the news conference whether racial tension was a factor in the shooting, Mayor Tom Barrett declined to comment on Ferrill's motive.

"Right now, there's an investigation going on, and I think it's premature to speculate on anything," Barrett said. "I think this is the time to be there to grieve and to support the families."

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About a year ago, the co-worker said, Ferrill started saying he believed brewery workers were coming into his home, bugging his computer and moving chairs around.

"I was: 'Are you serious, Anthony? What?' We all kind of joked about it, saying we should maybe get him an aluminum hat. Things just started getting weird. But he was dead serious about it," the co-worker said.

But another co-worker, Keith Giese, said Ferrill seemed fine when he saw him earlier this week.

"I never had a clue. I talked to him a couple of days ago and he seemed fine to me," Giese said. "I had no idea that there was a problem, that somebody could snap like that."

The five victims were identified Thursday as:

Dale Hudson, 60, of Waukesha, an electrician with Milwaukee Brewery since 2008.

Gennady "Gene" Levshetz, 61, of Mequon, a powerhouse operator with the brewery since 2008.

Jesus Valle Jr., 33, of Milwaukee, a powerhouse operator with Milwaukee Brewery since 2014.

Dana Walk, 57, of Delafield, a machinist with the brewery since 2004.

Trevor Wetselaar, 33, of Milwaukee, a powerhouse operator with the brewery since 2018.

As word spread Thursday that Ferrill was the shooter, co-workers and neighbors uniformly expressed shock.

"He was a very good electrician, a very good worker and I couldn’t say anything bad about the guy," said Phillip Rauch Sr., who retired in April after working with Ferrill for 15 years. "Every time I worked with him he was always in a good mood."

Ferrill was a licensed industrial journeyman electrician and a member of the International Brotherhood of Electrical Workers in Milwaukee. He served in the U.S. Coast Guard from 1987 to 1991 and was honorably discharged, according to Rick Flowers of Milwaukee County Veterans’ Services.

Ferrill received a VA loan to help purchase his three-bedroom ranch home in the 8200 block of West Potomac Avenue. He had lived there with his wife and family since 2004.

Ferrill had a silencer on one of his two guns. During Thursday's news conference, officials did not respond to a reporter's question about whether he held a permit to carry concealed weapons.

Opioid used to manage back pain

Ferrill had a long history of back pain that was made worse when he was in car accidents in 2009 and 2010, according to court records. He was a co-plaintiff with the MillerCoors LLC Health Benefits Program in a 2015 lawsuit in connection with the second wreck.

A report filed as evidence in that suit, written by Glendale physician Jeffrey Gorelick, stated Ferrill's back problems started about 25 years earlier. He would use Vicodin, an opioid-based pain killer, and Cyclobenzaprine, a muscle relaxant, when lower back pain flared up, Gorelick wrote.

Gorelick did not treat Ferrill or prescribe medications to him.

"In spite of the back pain, he works every day as an electrician and pushes himself to get through the day," wrote Gorelick, a consulting expert who filed the report in support of Ferrill's lawsuit. "However, he is known on weekends to sometimes spend most of both days in bed recovering to allow him to get to work the next week."

The physician quoted Ferrill as saying: "Anything involving low back stamina I can't do. Shoveling, bending over at work, stooping, awkward positions, lifting my daughter."

The report noted that Ferrill had three children; two who were in their 20s at the time and one who was 7.

Ferrill normally worked more than 50 hours a week, Gorelick wrote.

Ferrill underwent multiple shoulder surgeries and had been forced to take time off work intermittently for years, according to neighbor Erna Roenspies, who said she had become close to Ferrill and his wife during the 15 years they've lived on her block.

A few years ago, he told her that insurance investigators were parked in the neighborhood, watching to see if he was working around the house, which could affect his workman’s compensation claim, Roenspies said.

A gun collector

Police continued to occupy Ferrill’s home Thursday; detectives and officers occasionally emerged with items.

Police tape still surrounded the house, which has a playset in the backyard, as neighbors struggled to reconcile the helpful man they knew with the heinous act authorities say Ferrill committed.

Roenspies said Ferrill sometimes helped her around the house, especially after her husband of 60 years died three years ago. She last saw Ferrill about two weeks ago when he came to help her with a faulty hot water heater.

“He was like my son,” Roenspies said Thursday. “He was a person who would help anyone in the neighborhood. This, it’s a shocker. I still don’t believe it.”

She said Ferrill was a gun collector, putting the weapons together in his home. He told her it was his hobby.

“I said, ‘I hate guns. I don’t want to see them,” she said. And she said she never did.

Elizabeth LaPine has lived in the neighborhood for 11 years. She said she once saw what she believed to be a gun safe delivered to the home.

“I knew he was interested in guns,” LaPine said.

She said it was hard to believe Ferrill was the shooter.

“I would never believe it ... that he could do something like that,” LaPine said. “He didn’t give me the impression that there was anything wrong. It didn’t seem like there was anything different.”

Ferrill had a Doberman pinscher named Lucas, LaPine said.

“He loved that dog,” LaPine said. “He played ball with it in the street when there wasn’t much traffic. He’d throw the ball down the street and the dog would chase after it.”

LaPine said Ferrill walked the dog every day before leaving for work.

She said Ferrill looked out for his home and his neighbors.

“He had given me his phone number about a year ago,” LaPine said. “He said ‘If you see anybody messing around the house or anything like that ... give me a call.’ ”

Neighbor Patricia Dibb said she felt “shock, anger, sadness” when she heard about the shooting.

“Sadness for the families; sadness for his wife; sadness for his daughter,” Dibb said, holding back tears. “Sadness.”

LaPine said she also feels terrible for the families involved, including the Ferrills.

“If you’re mad at somebody or something, talk it out, don’t shoot it out,” LaPine said. “You’re just hurting so many families.”

Rick Barrett, Ashley Luthern, Mark Johnson, Rory Linnane, Talis Shelbourne, Mary Spicuzza, Maria Perez, Raquel Rutledge, Ricardo Torres, Bruce Vielmetti and Cary Spivak of the Journal Sentinel staff and Nick Penzenstadler of USA Today contributed to this report.

Contact Gina Barton at (414) 224-2125 or gbarton@gannett.com. Follow her on Twitter at @writerbarton.