LAKES OF THE FOUR SEASONS, Ind.—A hand grenade exploded as a family went through a grandfather’s belongings in Indiana, killing a man and wounding his two teenage children, police said.

The explosion occurred Saturday in a garage area at a home in Lakes of the Four Seasons, about 30 miles (50 kilometers) southeast of Chicago, the Lake County sheriff’s department said.

Bryan Niedert, 47, died and a 14-year-old boy and 18-year-old girl were taken to a hospital with shrapnel wounds.

“Investigators are still trying to determine elements of the case including, but not limited to: whether the device may have self-detonated due to its age or other factors, whether the pin was pulled or whether any other circumstances may have been involved,” the sheriff’s department said.