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SLIDESHOW > See pictures of fake & real bills

Dan Jackson/KREM.com

One of the fake $10 bills allegedly manufactured in a bathroom at River Park Square Mall.

SPOKANE--Detectives arrested a teenager they say was counterfeiting $10 bills in the family restroom of Riverpark Square Mall in downtown Spokane.

Detectives said mall security told them 19-year-old Calvin Robinson was noticed inside the mall's family restroom for more than an hour on Wednesday afternoon.

The security officers jingled their keys outside of a locked restroom stall to make it seem they were going to open it up when Robinson finally opened the door.

The officers saw a color copier on the floor and sheets of paper in the trash on which $10 bills had been printed.

The U.S. Secret Service was contacted and took over the investigation.

Robinson told detectives he was homeless and didn't have access to power with which to print counterfeit bills, so he went to the family restroom so he could use the electricity and a place to work uninterrupted.

Robinson said he wanted to print enough $10 bills to buy $90 worth of marijuana.

He said he spent $100 on the color copier and paper at a local Office Depot he used for the operation.

Robinson is in jail on a forgery charge. He has prior convictions for vehicle theft and possession of stolen property.