BILLINGS, Mont. (AP) — An anonymous donor is offering a $100,000 reward for information leading to the conviction of whoever is responsible for a double murder in Billings in November 1973.

Yellowstone County Sheriff Mike Linder announced the reward Wednesday in the deaths of Linda and Clifford Bernhardt. Both were 24. Officials say Clifford had been hit on the back of the head, both had been strangled and Linda was sexually assaulted.

Linder says the case is progressing and he hopes the reward will bring forward people who have information.

Linda's mother found the victims. The Billings Gazette reports the heat had been turned off in the house and the windows were left open as temperatures dropped to 6 degrees that night. A suitcase, Linda's underwear and some of her shoes were missing.