The story of the perpetually stolen motorcycles

Once upon a time, an international theft ring stole motorcycles from their owners in NYC.

Then, the NYPD caught them, and "stole" the bikes from the thieves.

Then, someone stole them from the NYPD.

http://www.dnainfo.com/new-york/20120906/red-hook/12-people-arrested-red-hook-drug-sweep

"All the bikes seized by the NYPD were supposed to end up in their Auto Crime Division facility in Queens, sources said.

It was not clear why this group of motorcycles wound up stashed in the box truck."

I'd say it's pretty clear.