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A cold-hearted thief is holding bike parts hostage and using strange ransom notes in an attempt to lure riders into buying back their stolen gear, Park Slope cyclists say.

A brazen crook — or team of crooks — snatched the wheels off six bikes near the corner of Sixth Street and Eighth Avenue last weekend, then taped hand-written messages to the naked frames, according to victims.

“They went on a complete spree,” said cyclist Johanna Clearfield. “It’s unbelievably nervy.”

Clearfield locked her blue mountain bike to a pole at the corner at 11:30 pm on July 14, then came back the next morning and discovered both wheels had vanished. A strange note with a phone number had been taped to the body of the bike.

“Whoever owns the bike and two stolen wheels, I caught the guy. I have the bike and wheels,” the note read.

Clearfield first thought a do-gooder had pulled a heroic move — though he clearly didn’t “have the bike,” as the frame was still locked to the pole.

But then she looked closer and noticed the note had been photocopied.

That’s when she spotted five more identical notes taped to other pillaged bikes and poles on the same block, leading her to believe the person behind the message was involved in the crime.

The mysterious note writer wants to sell the bike parts back to the victims or cash in on reward money, she claims.

Her theory may not be far off: cops arrested two teens accused of bike theft several blocks away on the same night, according to officers at the 78th Precinct. Police spotted the boys — who were traveling in a pack of four — cutting a bike lock with red clippers near Fifth Avenue and President Street just before midnight, about twenty minutes after Clearfield parked her $300 ride, according to investigators.

Victims say it’s unlikely the author of the message is a good Samaritan, claiming it would be almost impossible for a passerby to catch and detain a bike bandit mid-spree — then transport dozens of parts and wheels home on the same night.

Plus, the one-size-fits-all note is oddly generic and could have been penned before the crime even took place, said Clearfield, who has since blogged about the incident on Park Slope Patch.

Brooklyn Weekly tried calling the number on the note on Wednesday but nobody answered.

Clearfield now says she has just one request for the note author, whoever he may be.

“Can I get my wheels back now?” she said.

Reach reporter Natalie O'Neill at noneill@cnglocal.com or by calling her at (718) 260-4505.