MANDAN, N.D. (AP) — A North Dakota business where an owner and three employees were found slain this week reopened with a police presence on Wednesday, though authorities still haven’t said how they were killed.

State and local police later in the day searched in a field about half a mile from the business, though they did not immediately say whether the search was related to the case. Half a dozen vehicles, including a state Bureau of Criminal Investigation truck, were at the scene, parked near a snowbank in the field.

Police discovered the bodies early Monday at RJR Maintenance and Management in Mandan, a city just across the Missouri River from Bismarck. Police have classified the case as a “multiple homicide.” Investigators say they don’t know who the killer is, but that the person is not among the dead.

The mood at the company was somber as a police officer monitored the parking lot and workers quietly talked with one another outside before the company opened Wednesday morning. Company co-owner Jackie Fakler, whose husband was among the dead, also returned to work.

She and others declined comment, saying they were dealing with a difficult time. But on its Facebook page, the company thanked the community for its “generosity and support” and said donations of money, food and other items would go to the dead workers’ families.

Police have released few details about the case, including whether investigators have identified a potential motive. However, Police Chief Jason Ziegler said authorities do not believe the public is in danger.

The people who died have been identified 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.

According to its website, the family-owned 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.