A top aide to Maricopa County Sheriff Joe Arpaio has requested an investigation of the sheriff's second-in-command, Chief Deputy David Hendershott, and two of his allies, signaling growing concern among the sheriff's top hierarchy about the agency's management.

A memo written by Deputy Chief Frank Munnell and recently delivered to Arpaio alleges years of misconduct and mismanagement by Hendershott, who has directed day-to-day operations of the Sheriff's Office since 2008 and has been in the department's top echelon since the mid-1990s.

The alleged wrongdoing amounts to criminal activity in the eyes of Munnell, a longtime law-enforcement official.

The 63-page memorandum obtained by The Arizona Republic is the first clear inside account of a law-enforcement agency that is under investigation by the FBI and U.S. Attorney's Office for suspected abuses of power and has had considerable publicity about its failed corruption investigations into county officials and judges.

Munnell's memo has been turned over to the FBI and U.S. Attorney's Office for their probe. Both agencies declined to comment.

Munnell said Arpaio ceded control of the department to Hendershott after the sheriff won his last re-election campaign in 2008. Munnell pleaded for the sheriff to retake control of the agency.