Theranos founder Elizabeth Holmes takes the stand in her criminal fraud trial

Fallen Silicon Valley star Elizabeth Holmes took the witness stand late Friday in a surprising development in her criminal fraud trial. The former entrepreneur will attempt to refute the U.S. government's allegations that she bamboozled investors and patients into believing that her startup, Theranos, would reshape health care.

The decision to have Holmes testify so early in her defense was a bombshell development that carries considerable risk. Federal prosecutors made it clear that they are eager to grill Holmes under oath as they presented their case against her.

It's unlikely that prosecutors will get that opportunity until Monday at the earliest, when the trial resumes. The government's evidence included testimony from 29 witnesses, including former U.S. Defense Secretary and former Theranos board member General James Mattis, as well as internal documents and sometimes salacious texts between Holmes and her former lover, Sunny Bulwani, who also served as Theranos' chief operating officer.