UPDATE: Driver arrested in connection with fatal Rosemount crash involving boulder

A mother and daughter from Shoreview were killed Monday, July 9,  when their car was struck by a boulder that fell off a commercial truck in Rosemount, police say.

Karen Christiansen, 67, was driving a Toyota Avalon about 4:50 p.m., when a boulder weighing several hundred pounds fell off a southbound truck and hit the car, said Mitchell Scott, chief of the Rosemount Police Department.

Christiansen and her 32-year-old daughter, Jena Christiansen, who was in the front passenger seat, both died at the scene.

Scott described the incident as a freak occurrence.

"It's very rare, but it does happen," he said. "That's why it's so important to slow down and make sure loads are secure, because you're taking other people's lives in your hands."

Investigators have identified the driver of the truck and were working to locate him Wednesday evening, Scott said.