YONKERS (CBSNewYork) – Some first-class thieves have been ripping off the mail in Yonkers.

Yonkers Police say there were a spate of mail thefts that took place early Tuesday morning.

Seven mailboxes were robbed along Yonkers Avenue between 1:30 a.m. and 2 a.m., police said.

CBS2 has learned multiple police agencies have been rounding up suspects.

Sources tell CBS2 the suspects obtained at least one key- which has since been recovered – that makes the crime as easy as unlocking a door.

Wary customers are bypassing the mailbox right outside the Yonkers East post office and depositing their mail securely in the slot inside.

Surveillance video shows a suspect easily open the outside box, remove the bin, and dump dozens of pieces of mail into a bag held by a second suspect.

“He doesn’t jimmy the lock. He doesn’t. Just looks like somebody got the key,” Yonkers resident Henry Miller told CBS2’s Tony Aiello.

A post office source told Aiello the USPS has protocols to control who has access to the keys. Employees are supposed to sign them out – and then back in – on the days they need the keys to collect mail from the boxes.

More than a dozen locations have been hit in Westchester County.

Early Thursday, an undercover team of Yonkers Police grabbed three Bronx men, allegedly caught in the act at a mailbox on South Broadway.

“Three males approached the box, attempt to gain access. When stopped, each of the males had on their possession stolen checks,” Yonkers Police Commission Charles Gardner told Aiello.

You can imagine the major inconvenience for customers whose mail is stolen.

Josh Benjamin had thousands in business checks taken.

“They’re scaring me at the bank, telling me ‘Make sure you monitor, they’re whitewashing checks’ and this, that and the other thing. Hopefully, that doesn’t become an issue, but,” he told Aiello.

It’s called “check washing,” a process to remove information written on checks in ink. The checks are then altered and cashed.

Crooks are also happy to grab any cash they find in the mail they steal, some of it no doubt meant for moms this Mother’s Day, and recent college graduates.

Officials warn anyone who used mailboxes along that strip to send checks or checking account information to notify their financial institutions and make sure their bank accounts haven’t been compromised. Yonkers police also warn people to beware of the possibility of identity theft, late payment charges for bills sent through the mail as well as financial scams. Officials urge people to avoid using checks if online payment is possible, and if using a check to write and sign it with a gel-based pen, which resist check washing.

To learn more about how to contact credit bureaus to set up fraud alerts, click here.

Anyone with any information about the incidents is asked to call Yonkers Police at (914) 377-7900.