BRENTWOOD (CBSLA.com)  —  Police in Brentwood are asking the public if they can help them nab a series of mail thieves.

Security cameras in one building — the Regency Royale — caught one alleged thief who appears to have a master key to mailboxes. The mystery, of course, is how she obtained the master key in the first place.

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CBS2’s Greg Mills reported this suspect filled her big bag with mail and snagged a large package.

And then she fled.

“We felt rather vulnerable,” said condo resident Julie Nameth, “violated that someone could come in and get our mail.”

Nameth has lived in the building for 15 years and said she always felt safe. You need a key to get into the building and you need a key to use the elevator.

The suspect had no trouble gaining access to the building.

The alleged theft took place around 2 a.m. last Sunday while most residents slept upstairs.

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“Now I’m left with my fear because im concerned she or someone else will return,” said resident Judi Hochman.

The Postal Service left a collage of suspects involved in recent mail thefts around the Barrington area.

“The people in the photos the postal service gave us are not the same person who broke in here,” said resident Roberta Johnson.

In the Regency Royale theft, Mills was told security cameras also captured the suspect opening a lock box that has the master key inside.

She was confident enough, he reports, that she took more than three minutes and 30 seconds to load up all the mail.

Residents are left wondering how the woman was able to get a key to get into the lock box. They told Mills the only person who should have a key of this type is someone who works with or for the postal service.

Residents filed police reports. Police told the residents to also report the thefts to the post office.

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Mills said the president of the Homeowner’s Association was told he would be contacted between 48 and 72 hours and has not heard back yet from the post office.