The Wall Street Journal has this free article today on how Time Magazine's Matthew Cooper decided his interests were not the same as those of New York Times reporter Judith Miller. It's true that Cooper cooperated about Libby early on, as did Russert, Walter Pincus and Glenn Kessler, and then balked at getting a second subpoena for other sources. I've reported Judith Miller's take on that several times, most recently here.

The Wall St. Journal article mostly focuses on Cooper's lawyer's point of view, but this quote from Floyd Abrams, who originally represented both Cooper and Miller, is key:

But the deposition, held in the Washington office of Mr. Abrams's law firm, only whetted Mr. Fitzgerald's appetite. "Matt's testimony about Libby led Pat Fitzgerald to decide he wanted more information about others," Mr. Abrams explains. Specifically, the prosecutor wanted Mr. Cooper to confirm that Mr. Rove was a source of information about Ms. Plame. Within weeks, Mr. Cooper had a second subpoena in hand.

So, Fitzgerald knew it was Rove. He wasn't fishing.