One teenage boy has died, and two others were injured after playing with a World War II-era hand grenade, Interfax news agency reported on Monday.

The boys, two of whom were aged 10 and one 13, found the grenade in a backyard in the Kaluga region town of Zhizdra. One boy was killed immediately, while his two friends have been hospitalized with minor injuries, local police said.

The grenade belonged to a 65-year-old man who told investigators that he had found the explosive device many years ago, put it in a shed and then forgot about it. Later, he sold the house.

A criminal case has been opened against the man over “illegal possession of weapons or explosives.” He faces up to three years behind bars if found guilty.