HAYWARD -- Twin brothers from Washington state were in custody Wednesday afternoon after police said one of the men robbed a busy U.S. Bank branch.

Officers were called to the business at 31045 Mission Blvd. after they received a 911 call that someone had a gun inside the bank, said Sgt. Mark Ormsby.

It's unknown how much, if any, money was taken as police were still investigating the armed robbery as of about 3 p.m., Ormsby said.

Witnesses gave police a description of the armed suspect and, shortly after, officers found him standing at Prestwick Avenue and Saint Andrews Street.

The suspect told police he was looking for his twin brother who was supposed to be waiting for him in a car outside.

Shortly after, officers spotted the man's brother at Mission Boulevard and Garin Avenue and detained him for questioning.

"The suspect said his brother had no involvement and didn't know about the robbery," Ormsby said. "It's unclear his involvement at this time, but the brother remains in custody."

The names of the men were not immediately released. But Ormsby said the men appear to be in their early 20s and are from Washington state.

Check back for more details.

Contact Natalie Neysa Alund at 510-293-2469. Follow her at Twitter.com/nataliealund.