A 44-year-old man has been arrested in connection to a mass murder inside a North Dakota workplace, police said.
Four people were found dead Monday morning at RJR Maintenance & Management, a property management company in Mandan, police said.
A motive for the killings was not clear.
Chad Isaak, of Washburn -- about 40 miles from Mandan -- is being held on four counts of AA felony murder, Mandan Police said at a news conference Thursday night.
The causes of death have not been released, but the victims -- the owner of the company and three employees -- were all shot or stabbed, police said.
Isaak's car was identified at the scene of the shooting by surveillance cameras, officials said. Investigators later located the vehicle in Washburn.
He was arrested during a traffic stop Thursday, police said.
Evidence in the vehicle gave investigators enough probable cause to make an arrest, said Police Chief Jason Ziegler.
The location where the suspect lived was a mobile home park managed by RJR, but police are not sure if that is part of the motive, Ziegler said.
Isaak is being held at the McClean County Jail. He is scheduled to make an appearance in court Friday afternoon.
Among the victims were Lois Cobb, 45, and her husband, William Cobb, 50, who worked at the company.
"I don't know how it happened," Cobb's daughter, Briann Miller, told The Associated Press. "I'm left in the dark still. None of this makes any sense. All I know is my parents are gone."
Miller, of Illinois, told the AP her mother and stepfather moved from Illinois to North Dakota six years ago and recently purchased their dream home.
"They were true soulmates, "Miller told ABC Springfield, Illinois, affiliate WICS.
The other victims were owner Robert Fakler, 52, and employee Adam Fuehrer, 42, said police.
Ziegler said the crime "was very specific to the victims that were involved."
"I don't think any community across this great country could ever imagine something like this happen in their backyard," Ziegler said, calling the crime "devastating" for the community.
The chief called RJR Maintenance & Management a "reputable company in our area."
There were security cameras inside the building but the chief did not say if the crime was on video.
ABC News' Darren Reynolds contributed to this report.
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