San Francisco Police Department Sergeant Matt Friedman is the Sisyphus of San Francisco.

Since 2013, Friedman has been fighting bike theft not just on the streets but on Twitter as @SFPDBikeTheft, where he posts and receives tweets on San Francisco's epidemic of bike theft. And by epidemic, I mean that every three hours, a bike is stolen in San Francisco, ABC 7 reported last year — and that statistic refers only to the ones that people bother to report to police, so the number is likely far higher.

Most of the theft victims never see their bikes again, as most are taken to "chop shops," where the bikes are swiftly dismantled and resold. We've all spotted that brazen urban phenomena — a stack of disparate bike parts seemingly-randomly piled together, often by folks who seem unlikely to have gotten the numerous cycles through legitimate means. "Pretty sketchy," you might think as you pass by, wondering why the cops don't give these encampments a little more scrutiny.

Here's an example:

Catching the chop shop staffers for theft is tough, ABC 7 reported in 2015, because the workers take "bikes apart and mixed the pieces to build new bikes. The bikes were painted, so they couldn't be easily identified by the owners."

"There's new handlebars, there's stickers on the frame, the frames are painted over, serial numbers are sometimes scratched off, there's a different wheel set on there now," Friedman told ABC 7.

"People from all over the city come to these chop shops and they exchange stolen bikes usually for drugs or money or money to buy drugs...They happen all over the city, unfortunately."

SFPD regularly sweeps homeless encampments for chop shops, only to see them pop up again afterwards, Friedman says. But that won't stop him from rolling that rock back up that hill again and again and again. His latest push against chop shops, he said via Twitter Sunday evening, will be in the Mission District as of noon today  a sweep that follows a weekend theft of $20,000 in new bikes from Low Bicycles, via a smash-and-grab.*

We will be rolling around the Mission tomorrow dealing w/ chop shops starting at 1200. Tweet at us if u see something u want us 2 checkout — SFPD Anti Bike Theft (@SFPDBikeTheft) August 15, 2016

Low Bicycles said in an Instgram post, "We know that it was a group from the bike chop shops that live around Division and Harrison street, so keep an eye out THESE ARE UNIQUE BICYCLES."

Friedman says police will begin by heading "down Division and most likely going straight over to Best Buy," and from there it's anyone's guess, as San Franciscans are asked to Tweet at his account with any Mission area chop shops they'd like to see investigated.

You can respond to his tweet with the locations here, and follow SFPDBikeTheft here. Know of a Mission chop shop, but refuse to use Twitter? Then drop me a line with all the relevant information at [email protected] and I'll tweet on your behalf.

Previously: Video: Thief Steals Bike On Valencia In Broad Daylight



*This post has been updated with details on the Low Bicycles robbery.