Authorities are still working to determine whether the robberies that happened Monday at six 7-Eleven locations are connected, police said.

"Our hearts remain with the victims and their loved ones, and our focus continues to be on Franchisee, associate and customer safety," a 7-Eleven corporate spokesperson told CNN on Tuesday. "With that in mind, we have encouraged stores in the Los Angeles area to close again tonight."

The robberies unfolded early Monday morning across stores in Santa Ana, La Habra, Brea, Riverside, Upland and Ontario, California, according to police.

Police in Brea and La Habra are "confident" the shootings in their jurisdictions are connected, saying they're in communication with other agencies.

"Our hearts are with the victims and their loved ones," 7-Eleven said in a statement

A store employee at the 7-Eleven in Brea was killed after he was shot, the police department said Monday. Another person was killed at the 7-Eleven location at Santa Ana, a police spokesperson told CNN.

"Based on the photo released we believe it is the same suspect," the spokesperson said.

Two other people were shot during the robbery at the location in La Habra and taken to the hospital, police said during a news conference.

Meanwhile, a 7-Eleven customer was shot at after a gunman entered the store in Riverside, "brandished a firearm and robbed the clerk," a police spokesperson said. That victim was taken to a local hospital, where they were in "grave condition."

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

In Upland, police said no shots were fired and no one was injured during the robbery at 7-Eleven. And in Ontario, California, the gunman demanded money while showing a gun and didn't fire his gun.