ST. LOUIS, Missouri (CBSNEWS) — An off-duty police officer shot and killed a home invader in suburban St. Louis on Saturday evening, and family say the two had recently had an argument about the growing unrest over police violence.

Police say the off-duty officer, who has not been named, was home when the deceased suspect rang the doorbell on Saturday evening.

KMOV-TV reports the suspect was known to the family. At the time of the incident, the police officer was home with his wife, mother-in-law and two children. They ran upstairs to hide when the suspect appeared.

The suspect, identified as 20-year-old Tyler Gebhard, then grabbed a concrete planter and threw it through a window in the rear of the house when he was denied entry to the home.

Once inside, the off-duty officer shot him. Gebhard was pronounced dead at a local hospital.

Police told KMOV the man had emotional issues and had issued threats to the family online before the shooting.

An uncle of Gebhard’s, Patrick Brogan, of Waterloo, Illinois, told The St. Louis Post-Dispatch that Gebhard and the officer had been arguing on Facebook. He said Gebhard, who was biracial, empathized with the objectives of the Black Lives Matter group.

Police Chief Jon Belmar says the officer is on leave.