Coleen Rowley's journey from obscure FBI agent to star Senate witness began during three sleepless nights.

Just weeks ago, she was jotting down notes on FBI bungling for a Senate inquiry of intelligence failures before Sept. 11. The notes became a letter to Director Robert Mueller. The letter became a symbol of FBI problems. The author became an object of Senate praise.

Flashes from 20 cameras exploded as the veteran Minneapolis agent was escorted to the oblong witness table by Sen. Charles Grassley, the Iowa Republican who is the champion of federal government whistle-blowers.

The 47-year-old mother of four never flinched, but did seem nervous at first as she sat alone before the senators, large glasses perched on the edge of her nose. There was only one temporary nameplate on the table: "Agent Coleen Rowley."

"I never really anticipated the impact," she said of the memo that accused FBI headquarters personnel of impeding an investigation of accused terrorist Zacarias Moussaoui.

Before a national television audience, Rowley disregarded her prepared statement and ad-libbed in a confident voice, speaking of the need for a changed FBI culture that tolerated internal critics.

Rowley said she was watching earlier in the day during Mueller's testimony, when senators demanded that he protect her from retaliation. Mueller had made the promise before, and did so again.

Sen. Arlen Specter, R-Pa., told Rowley that if FBI officials failed to keep the promise, "This committee is prepared to make sure they do."

Rowley said she has received hundreds of e-mails and phone calls from active and retired agents, supervisors and prosecutors.

"Lots of agents told similar stories about cases that had never gotten anywhere," she said.

Rowley said she did it in part for her kids, because she wanted to make sure the FBI did everything possible to protect them from terrorism.

Grassley said the star witness came to tell the truth. For some in the federal government, he said, that would be a sin.