MANDAN, N.D. (AP) — A person of interest has been detained in the investigation into the killings of four people at a North Dakota business, police said Thursday evening.

KVLY reports,  Investigators have arrested 44 year old Chad Isaak on suspicion of killing four people in Mandan on Monday.
Authorities say Isaak faces four counts of AA felony murder.
The Mandan Police Chief Jason Ziegler says the four victims had been stabbed and shot.
Officials stopped Isaak during a traffic stop in Washburn, ND and say evidence in the vehicle and on Isaak prompted them to arrest him.
Police Chief Ziegler says the motive for the killings is still unknown.

Mandan police in a news release cited a tip that led them to Washburn, about 35 miles (56 kilometers) north of Mandan. The department did not release further information, but a news conference was planned for later Thursday.

Deputy Chief Lori Flaten confirmed earlier Thursday that a search conducted Wednesday in a field about half a mile from the business was related to the investigation. She said state and local police at the scene were “looking for potential evidence,” but she didn’t elaborate.

The bodies of an owner and three employees were found early Monday at RJR Maintenance and Management in Mandan, a city of 22,000 people just across the Missouri River from the state capital of Bismarck. Police haven’t said how the four were killed or publicly suggested a possible motive. But they said the attack “was specific to the victims,” and they didn’t feel the public was in danger.

Earlier Thursday, police declined to release details of a 911 call that alerted authorities to the slayings. The Associated Press and other media outlets asked for audio and a transcript of the 911 call, but police denied the requests, citing a provision of the state’s open records law that allows authorities to withhold such information during an active investigation.

Police have identified the dead as Robert Fakler, 52, co-owner of the property management business; employee Adam Fuehrer, 42; and married workers Lois Cobb, 45, and William Cobb, 50. A combined memorial service will be held Tuesday at Bismarck Community Church, according to Eastgate Funeral and Cremation Service.

According to the website for the family-owned property management business, the company has been handling commercial and residential properties in the area for more than 20 years. Its services include collecting rent for landlords, paying mortgages, re-renting apartments, building and grounds maintenance, lawn care and snow removal. It also rents out storage units.

The RJR building is somewhat isolated despite its location in a business district near a busy main road known as The Strip. A large empty lot sits in the front, a golf course in back and a soccer complex to one side.

Mandan had not had a homicide since November 2016, and had only three in the past six years. In that time period, neighboring Bismarck, which has about 73,000 residents, had seven homicides.