OAKLAND, Calif. - Postal workers are outraged after a string of robberies in the East Bay.
Since Saturday, three mail carriers have been robbed and there was one attempted robbery.
And in all of the cases, the thieves are going after mailbox keys.
There were three cases in Oakland and one in Berkeley.
The most recent took place Wednesday afternoon on Spencer near 75th Avenue in East Oakland.
Postal Inspector Matthew Norfleet told KTVU three women jumped out of a dark colored four door vehicle and confronted the mail carrier.
"One woman held the carrier. The others took her equipment and then they sped away from the scene," said Norfleet.
"That was really sad. I couldn't believe it," said one witness who wished to remain anonymous and that the carrier had parked her mail truck by a no parking sign when she was robbed.
"She was screaming: help me, help me and I think they stole her keys ," said the witness.
"These are standard issued mailbox key chains that the letter carriers have," said Norfleet as he held out a chain that carriers wear to carry mailbox keys.
The postal inspector said in all the robberies, the thieves stole the keys the carriers wear on a chain. They are keys that open people's mailboxes.
"People are stealing the keys in order to steal mail," said Norfleet.
"Just worried. It's troubling," Oakland resident Derrick Bonderud said. A thief had used a key to access his family's mailbox and others in his apartment complex last fall to steal credit cards and other sensitive information.
"I was wondering how they were getting the keys. It makes sense that they're robbing the mail carriers. This is the first I've heard of this," said Bonderud.
The postal inspector said in at least three cases, the thieves targeted a female carriers.
Investigators are reviewing surveillance videos.
They say the suspect descriptions and the methods vary, and it's unclear if they are part of an organized crime ring.
People who've had their mail stolen should contact the U.S. Postal Service.
"If they're aware of their checks being stolen and cashed or their credit cards being stolen and used out of the mail to please don't forget to report it to postal inspector because that could be a valuable clue for us to work back to the person who stole the keys," said Norfleet. .
The postal inspector said the mail carriers' injuries are minor.
An assault on a mail carrier is a federal crime, punishable with up to 8 years in prison.
The U.S. Postal Service is offering up to a $50,000 reward for information leading to an arrest and conviction.
The Postal Service is urging anyone with information about the robberies and other postal related crimes to call U.S. Postal Inspector Dispatch at 1-877-876-2455