A McKinley High School special-education assistant pleaded guilty yesterday morning to four counts of sexually assaulting a student described by the prosecutor as "mildly mentally retarded."

Gregory Keau, 30, admitted to assaulting the victim at the school in 2007 and 2008.

Deputy Prosecuting Attorney Thalia Murphy said her office will ask for consecutive terms of imprisonment totaling 22 years behind bars.

Circuit Judge Michael Town will sentence Keau on Oct. 1.

In May, another school employee entered a classroom and witnessed Keau having sex with the student.

The victim told police later that Keau also assaulted her in 2007 when she was 16.

Department of Education officials said a criminal background check of Keau was conducted before he first began work at McKinley in 2001. It showed a 1999 conviction for driving without a license. A subsequent conviction for third-degree assault in 2003 was not reported to the school.

Keau pleaded guilty yesterday to two felony counts of second-degree sex assault and two misdemeanor fourth-degree sex assault charges.

Murphy said she will ask the court to sentence Keau to serve 10-year consecutive terms for each felony count plus consecutive one-year terms for the misdemeanor counts.

Keau was represented by Deputy Public Defender Lee Hayakawa.