Ryan Kilian was exchanging texts with his girlfriend, Jena Christiansen, on Monday afternoon when suddenly the messages stopped.
He soon learned the reason why: Jena and her mother, Karen, were killed when an 800-pound boulder tumbled from a truck passing on the other side of the road and smashed into their vehicle.
Both women were pronounced dead at the scene in Rosemount. The truck was nowhere to be found.
On Wednesday night, police located who they say was the driver at an Inver Grove Heights home. The suspect was being held Friday in Dakota County jail and has been charged.
"It's just tremendously sad for the family," said Rosemount Police Chief Mitchell Scott. "This is something that could have been prevented."
A representative of the Christiansen family said they weren't ready to talk. But in a series of messages Thursday, Kilian said he was heartbroken.
"How does this happen / Jena Christiansen, you are my world / Wake me up from this nightmare," he wrote on Facebook Wednesday.
Kilian said that both women were "loving people," and that Karen Christiansen had been kind and welcoming to him. Jena was quirky and sarcastic, he said, often making him laugh so hard he cried.