Dozens of checks mailed to the office, totaling millions of dollars, have been stolen and altered through a fraud called "check washing," officials said. An investigation is underway.
More than 3,000 delinquent letters were going out to Napa County residents who haven't paid their property taxes on Thursday. Napa County Treasurer and Tax Collector Robert Minahen knows some of them DID pay, but his office never received the check.
"We've had between 30 and 50 property tax checks stolen. We expect this to get worse before it gets better." Minahen said.
The stolen checks, totaling between $1 and $2 million, were cashed right away, but not by Minahen's office. This includes a sizable check from a Napa Valley vineyard owner for $225,000.
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It's called check washing. Criminals steal the checks and then alter the payee information -- in this case, a Florida LLC. Minahen said this fraud goes beyond someone fishing envelopes out of a mailbox.
"It appears somewhere between the Oakland main processing center and our office, these checks are being intercepted and stolen," Minahen said.
But how? The FBI and U.S. Postal inspectors are trying to find out.
"Unfortunately, there's no limit to the means criminals will use to try to get other people's property out of the mail," said U.S. Postal Inspector Mathew Norfleet.
We were there when Tom Layman from Napa stopped by the tax collector's office after, he says, his property tax payment disappeared.
"On April 2, I wrote a check and put it in the mail. This morning, I called. They said they never got it," Layman said.
The check washing theft is almost identical to one 7 On Your Side investigated in Santa Clara County last winter: property tax checks stolen from the mail.
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The Napa Tax Collectors office is vowing work with banks to help refund victims and cancel late fees. In the meantime, the office urges taxpayers to make payments online.
It doesn't help all property tax payment collection envelopes are bright green, a bit of neon sign to thieves.
"Green has been our color for years. We won't use it next year," Minahen said.
The office posted on social media, urging taxpayers who paid by mail to check their bank statements right away.
U.S. Postal inspectors say if you've been a victim, call the 24-hour hotline: 877-876-2455.