HONOLULU -- A McKinley High School teacher's aide on Tuesday pleaded not guilty to sexually assaulting a special education student.

An Oahu grand jury indicted Gregory Keau last week. Authorities charged him with sexually assaulting a 17-year-old special education student in a McKinley classroom earlier this month.

Another school employee witnessed the incident and reported it, according to officials. The teen told authorities that it was the second time Keau sexually assaulted her.

Keau is being held at Oahu Community Correctional Center on $75,000 bail.

Trial is scheduled for the end of July.