Ancelmo Osmin Diaz Credit: Via Montgomery County police

An employee of Gaithersburg High School allegedly sexually abused three of his family members, including two juvenile girls, over the course of years in his Gaithersburg home, school officials said Wednesday.

Montgomery County police arrested Ancelmo Osmin Diaz, 59, on Tuesday and charged him with 14 counts of sexual abuse, assault and sex offenses.

“The charges are not related to his role as a Montgomery County Public Schools’ employee and the alleged abuse did not occur on school property,” Gaithersburg High Principal Christine Handy wrote in a letter to parents in which she described the alleged victims as family members of Diaz. “Nonetheless, the alleged behavior described in these charges is upsetting and unacceptable.”

MCPS hired Diaz in 1995 and he worked exclusively at Gaithersburg High School, where he was a building services employee, Handy wrote. He has been placed on administrative leave.

Diaz, of Longmeadow Drive, is accused of inappropriately touching one juvenile girl for about three years, police said. Another girl told police Diaz had inappropriately touched her for five years, and a woman told investigators he had inappropriately touched her when she was 18. The victims spoke to police this month. Police did not specify the age of the victims when the abuse allegedly occurred.

Diaz allegedly “made statements partially admitting” to the touching, police wrote in a press release Wednesday.

On Tuesday, Diaz turned himself in to police. He was charged with six counts of sexual abuse of a minor, one count of second-degree assault and seven counts of fourth-degree sex offense. He is scheduled for a June 1 preliminary hearing in Montgomery County District Court in Rockville.

Police have asked parents of students at Gaithersburg High School to talk to their children about their interactions with Diaz and to call 240-773-5400 if they believe their child was victimized.