SAN DIEGO -- Police Sunday investigated three weekend commercial robberies across the city, undertaken by similarly-described suspects, to see if they might be related.

In each case, a man with similar appearance walked into a chain store and claimed to have a gun, but none was seen.

Police said one took place shortly before 2 p.m. Sunday at the Payless Shoe Source at 662 Dennery Road on Otay Mesa, where a man walked in and pointed to where he said he had a gun.

About an hour earlier, a man held up the Staples store at 4240 Kearny Mesa Road. He was last seen running around to the back of the building, police said.

At around 10:30 p.m. Saturday, a man simulated a handgun and demanded cash from a clerk at the Albertson's supermarket on Lake Murray Boulevard, according to SDPD Officer David Stafford.

The suspect in that hold up was described as a 30-year-old black male, about 6 feet tall and between 170 and 200 pounds, Stafford said.