The incident happened around 2 p.m. Monday in the area of Durfee Road and Garvey Avenue in El Monte.
A person described as a male adult suspect was pronounced dead at the scene, according to the Los Angeles County Sheriff's Department.
Few other details were immediately available about the incident, but the LASD says its investigators are assisting El Monte police.
Anyone with more information was asked to contact LASD investigators at (323)890-5500 or provide anonymous tips through Crime Stoppers at (800)222-TIPS.