For many people, Bike to Work Day (which is today) is a reason to put air in their bike's tires and see if their chain is too rusty to get them to work on time. And as a growing list of photographs shows, many people who follow NPR online also ride to work.

The prosecution's star witness underwent a withering cross-examination on Thursday at Roger Clemens' perjury trial. Clemens, a seven-time Cy Young Award winner, is charged with lying to Congress when he testified that he never used performance-enhancing drugs. Brian McNamee, his one-time trainer, is the only witness who has firsthand evidence that contradicts the baseball-pitching ace.

Earlier this week, guided by the prosecution, McNamee testified in agonizing and repetitive detail about how he injected Clemens with steroids and human growth hormone between 1998 and 2001.

Documents have been released in the investigation of George Zimmerman's shooting of Trayvon Martin. Zimmerman, a neighborhood watch captain, shot Martin, an unarmed teen. He's claiming self-defense. Robert Siegel talks to Greg Allen.

From WHYY

A new law in Pennsylvania has doctors nervous.

The law grants physicians access to information about trade-secret chemicals used in natural gas drilling. Doctors say they need to know what's in those formulas in order to treat patients who may have been exposed to the chemicals.

But the new law also says that doctors can't tell anyone else — not even other doctors — what's in those formulas. It's being called the "doctor gag rule."

'I Don't Know If It's Due To Exposure'

A huge trove of documents has been released by prosecutors in the Trayvon Martin case. Among the biggest revelations so far is that the autopsy reveals Martin had THC in his system. But police said the shooting was "ultimately avoidable."

ABC News, which is digging through the documents, reports:

"The autopsy report shows traces of the drug THC, which is found in marijuana, in Martin's blood and urine.