CHAPEL HILL, N.C. — A judge on Tuesday refused to lower the bond set for a former Chapel Hill teacher charged with 20 sex-related offenses.

David Campbell Jones, 46, of 113 Hampton Court in Chapel Hill, was charged Monday with 20 counts of second-degree sexual exploitation of a minor. He is being held in the Orange County Jail on a $500,000 bond.

Jones, a science teacher and coach at Phillips Middle School before resigning last month, was initially arrested on Aug. 9 on a charge of solicitation of a child by computer to commit an unlawful act. Authorities said he had corresponded with a 15-year-old boy over the Internet, and they arrested him as he walked up to the boy's home.

When he was arrested, Jones was carrying condoms, personal lubricant and a digital camera, according to a search warrant.

The latest charges stem from a search of Jones' computers that were seized from his home and the school following his arrest, authorities said. Investigators found more than 3,400 videos and more than 30,000 images on the computers that they said depicted other crimes, such as children as young as 5 engaging in sex acts.

Jones also has been charged in Wake County with taking indecent liberties with a child last April.

He was released on bond in late August after his lawyer argued that the $1 million bond initially set for the Internet sex offense was excessive.

The investigation of the case is continuing, authorities said.