Sheriff's officials launched an internal criminal investigation Tuesday into the alleged beating of a Los Angeles County jail inmate by deputies that was witnessed by an ACLU staffer last month.

Spokesman Steve Whitmore said the sheriff's office of independent review will look into the incident, in which two deputies allegedly hit and kicked an unconscious man on Jan. 24.

He said an administrative review was under way when ACLU attorney Esther Lim filed a court declaration Monday describing the brutal beating of inmate James Parker, which she saw through a window while meeting with another inmate at Twin Towers jail.

The sheriff's log entry on the use-of-force incident said Parker punched deputies and fought until he was hit with a stun gun.

In the court declaration, Lim said the two deputies beat Parker for two minutes even though he was unconscious and not fighting back.

"Mr. Parker looked like he was a mannequin that was being used as a punching bag," Lim wrote. "I thought he was knocked out, or perhaps even dead."