Mr. Murphy is currently preparing for interviews about the intelligence office with the inspector general of the Homeland Security Department and the House Intelligence Committee. The committee has been investigating the department’s intelligence branch since July after the office authorized analysts to collect information on protesters who damaged statues and monuments. The committee has received internal documents and is preparing to interview witnesses on the agency’s deployment of tactical agents to Portland, Ore.
Representative Adam B. Schiff on Friday said in a letter the committee had expanded its investigation into a “wider range of reported abuses, deficiencies, and problems, including allegations of improper politicization of intelligence and political interference.”
Mr. Murphy is expected to testify in a closed-door session with the committee on Sept. 21.
He has gone from accused to accuser in a matter of weeks. Previous witnesses against the Trump administration, such as Alexander Vindman and Marie Yovanovitch, have been painted by critics of the president in golden hues. Mr. Murphy is more complicated: Last month, Representative Adam B. Schiff of California, the chairman of the Intelligence Committee, said he was concerned Mr. Murphy misled Congress over the office’s intelligence gathering methods during the unrest in Portland.
Mr. Murphy, a conservative Republican who supported Mr. Trump in 2016, saw the senior intelligence position at Homeland Security as a logical next step for his counterterrorism career, former officials who worked with him said. His work at the F.B.I. earned him the nickname T-1000, after the almost indestructible, relentless android in the movie “Terminator 2.”
But his brusque style and penchant for going alone over repeated warnings from superiors to hew more closely to the rules ultimately stalled his career at the F.B.I. before he could land a plum assignment running a field office, a former senior law enforcement official said.
In interviews, former colleagues saw him as a “freelancer” who was determined to see investigations to the end, even if it meant ignoring unwritten rules of an institution. That reputation led some in F.B.I. leadership and the Justice Department to sour on him, according to interviews with nine former colleagues who requested anonymity to speak candidly about the whistle-blower and the Homeland Security intelligence office.
Mr. Murphy’s commitment to collaborating with state and local law governments also made the Office of Intelligence and Analysis at the Homeland Security Department attractive.