New Castle police are asking people in the area to be extra careful when they are putting checks or money in the mail.

According to New Castle police, they've received reports of at least eight instances where checks have been stolen from mailboxes throughout the area.

MORE: 8 tips to help prevent mail thefts

They say thefts have occurred from standard and tamper-proof residential mailboxes. The checks are stolen then altered for large sums and cashed out.

Investigators say more than $140,000 has been stolen so far.

"They'll alter the checks to a different name, use a fake ID or cash the check at an ATM where no one's really watching, and they're able to access the funds," says New Castle Detective Anthony Chiarlieti.

Police say thieves especially look for mailboxes that have the little flag raised to alert letter carriers there's something inside. Unfortunately, they say that also lets crooks know there's something inside the box they may want.

Detectives have been canvasing the area to see if anyone may have caught the thieves on their home surveillance systems.

In the meantime, they say it's best not to leave mail in your home mailboxes. "We want residents to be aware of this, and to bring mail directly to the post office. Or if they are paying something like a landscaper, or contractor, maybe hand-deliver the payment instead of leaving it in the mailbox," says Chiarlieti.

Police suggest that if you need to mail a check, don't put it in your mailbox but go to the post office and put your envelope in the mail slot inside the building or use online banking services

They say people should be on the lookout, and if you see someone by your mailbox that's not your letter carrier to let them know.

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