Police are turning to Facebook and bank records to try to identify a motive for why four people were killed at a North Dakota business two months ago.

Mandan Police Deputy Chief Lori Flaten told the Bismarck Tribune that police are "trying to cover all the bases" in their investigation of the April 1 deaths of RJR Maintenance and Management co-owner Robert Fakler and three workers, who authorities said were shot and stabbed.

Chad Isaak, a chiropractor who lived at the mobile home park managed by the business, is charged with four counts of murder and other offenses in the case.

Isaak's attorney, Rob Quick, declined to comment on the case.

Court documents show police have sought search warrants for Isaak's personal and business bank records, as well as victims' Facebook accounts.

Flaten said the connection between the business and Isaak's home would need more reasoning to be considered a motive.

"Maybe we'll never find a motive," Flaten said.

The deputy chief wouldn't comment on how that could affect Isaak's prosecution.

Burleigh County State's Attorney Julie Lawyer said that generally, motives aren't necessary for criminal convictions.

"It's not that we are required to prove it, but it can be helpful to the jury if that's there, if they have doubt as to the person doing it," Lawyer said.

Police have obtained several items from the crime scene at the property management company in Mandan, a town of 22,000 near the state capital of Bismarck. They also searched Isaak's home and business in Washburn, according to affidavits and search warrant receipts.

Court records show investigators have found evidence that suggests Isaak tried to avoid detection by picking up shell casings, changing his clothing and cleaning a knife and gun with bleach.

Isaak's preliminary hearing is set for Aug. 12.

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Information from: Bismarck Tribune, http://www.bismarcktribune.com