The spy agency's charter expressly denies it any domestic police powers, and it has historically confined itself to overseas operations.
The investigation was opened following an Associated Press report that said the CIA was aiding the police department. Petraeus said the agency placed an "adviser" in the department to help with information-sharing operations.
"Indeed, there is an adviser there who tries to ensure that there is sharing of information as that is essential and advisable, noting that we are very sensitive to the laws and civil liberties [concerns]," Petraeus said during a rare joint hearing of the Senate Intelligence Committee and House Intelligence Committee.
Director of National Intelligence James Clapper, who also testified at the hearing, said he did not believe it was "good optics" to have a CIA analyst embedded in the police department. But Clapper said he disagreed with criticism that the U.S. government's counterterrorism efforts inside the United States are out of control.
"I do not believe there is, quote, too much domestic surveillance," Clapper said.