An unsecured boulder fell off of the back of a truck and killed a mother and daughter in Minnesota.

Karen Christiansen, 67, and Jena Christensen, 32 were pronounced dead on the scene on Monday, according to officials. After taking testimony from witnesses, detectives with the Rosemont Police Department were able to identify and arrest 33-year-old Joseph Czeck, the alleged driver of the vehicle, on Wednesday.

Czeck is facing charges of criminal vehicular homicide and leaving the scene without calling authorities or lending aid, according to RPD Chief of Police Mitchell Scott.

Investigators believe that the boulder was not sufficiently secured to Czeck’s truck.

“If your load is not secured, if something happens because you’re negligent, you’re responsible,” Scott told NBC News.

While detectives initially estimated the boulder to be about 800 pounds, after weighing the boulder it was found to be about 1100 pounds, Scott said.

“We have a lot of info we were able to obtain, a lot of info from witnesses,” Scott said. “We’re just kind of putting that all together, making sure we’re doing our due diligence and doing a thorough investigation.”