HOUSTON -

A registered sex offender has been accused of taking inappropriate photographs of cheerleaders at a competition in San Antonio, including some girls from the Houston area.

"We had 300 athletes at this meet," said Edgar Ruiz, a coach for Houston's All Star Revolution.

The cheerleaders were at the Cheer Power Southern Championship at the Alamodome over the weekend. The father of one of the Houston cheerleaders spotted someone suspicious in the crowd.

"I was actually sitting right behind the gentleman filming and thought it looked kind of odd," said Troy, who asked that KPRC Local 2 not reveal his last name. "I noticed he was zooming in to areas that he shouldn't have and noticed that while he was zooming in, he was taking still pictures while he was videoing."

Troy, who had a 9-year-old daughter in the competition, said the man was zooming in on the girls' pelvic areas. He tracked down an off-duty San Antonio police officer, who quickly put a stop to it.

"He just tapped the individual on the shoulder and said, 'You need to get your stuff and come with me,'" Troy said.

Police identified the man as 60-year-old Andrew Sanchez, a registered sex offender.  He was convicted of possession of child pornography in 2008. He has now been charged with improper photography.