LOS ANGELES (AP) — Two people were killed and three were wounded in shootings at four 7-Eleven locations in Southern California early Monday morning, authorities said.

At least three of the four shootings are believed to be linked to the same lone gunman.

The shootings appear to have occurred after predawn robberies or attempted robberies at the four convenience stores on July 11, or 7/11 — a day when the national 7-Eleven brand is celebrating its 95th birthday by giving out free Slurpee drinks.

“Our hearts are with the victims and their loved ones,” 7-Eleven, Inc. said in a statement. “We are gathering information on this terrible tragedy and working with local law enforcement.”

It wasn’t immediately clear to investigators what prompted the shootings in the cities of Riverside, Santa Ana, Brea and La Habra, or why the violence occurred July 11.