The first robbery occurred at 10:42 p.m. Tuesday as a 63-year-old woman was walking on Willow Pass Road near Farm Bureau Road.
The woman told police she heard someone running up behind her and then a man grabbed her purse, Cerletti said.
She lost sight of the man when he ran into the parking lot of a 7-Eleven store.
The woman started yelling and a man who had been in the parking lot asked her if she had just been robbed.
Although he didn't see the robbery, the man told police that he saw a man run into the parking lot and jump into a gold or light brown four-door sedan with two other males inside.
Both the victim and the witness said the man was wearing a black sweatshirt with the hood pulled up over his head, a black bandana over his face and dark pants.
When the alleged thief got into the car, however, he took off the bandana and the witness was able to get a good look at him, Cerletti said.
While police were responding to the first robbery, they received a second call from a man who said he had just been beaten and robbed on Clayton Road near West Street.
The man had been riding home from work on his bicycle when three males knocked him off his bike and one pistol-whipped him with a handgun, causing significant cuts and bruises, Cerletti said.
As the victim was down on the ground, the three thieves allegedly punched him with their fists while going through his pockets.
They stole his wallet, his cell phone and his backpack. The victim then saw the trio get into a gold sedan, Cerletti said.
After they left, the victim got back on his bike, rode to the nearest pay phone and called police.
A short time later, police spotted a gold-colored sedan with three occupants inside that matched the descriptions the two victims had provided.
Officers stopped the car and found the second victim's cell phone and items from the first victim's purse, Cerletti said.
The suspects, two 18-year-old men, one from Oakland and one from Hayward, and a 17-year-old boy from Oakland were arrested and taken back to the station.