DENVER (KDVR) — Commerce City police are investigating after a woman discovered a mason jar in her yard that later exploded on her.

According to Commerce City Police Public Information Officer Joanna Small, the incendiary device was found on May 15 in the 6700 block of East 72nd Avenue. She reported the exploding jar overnight Sunday into Monday.

She said that when opened, the mason jar released an “unknown pressurized gas” that burned her face and led her to seek medical treatment. The police department said the jar was also filled with debris and nails and had a letter addressed “Too to my enemies.”

A Commerce City public information officer told FOX31 that the woman’s injuries were minor and that the victim believes the jar was made by someone she knew.

The Adams County Bomb Squad told the Commerce City Police Department that since the jar is now depressurized, it was safe to be placed in the police department’s evidence facility.

Small said that the investigation into who made and left the device was ongoing as of Monday.