OAK HARBOR, Wash. -- A 21-year-old babysitter here has been charged with 30 sex crimes, and police fear there may be additional victims.

Police said Nathan Martinez gave a partial confession during which he admitted to just some of the crimes they've uncovered. Martinez admitted to molesting three boys and girls between the ages of 3 and 12 since June 2007. He had been babysitting the children at the time.

However, ten children have told their parents Martinez had touched them, according to the document of probable cause. Not all of these children had been babysat by Martinez.

"He admitted to those three inappropriate sexual contacts, but by the next day we were at eight victims and more instances, more serious instances of offenses (including) child rape," said Oak Harbor Police Chief Rick Wallace.

The investigation began when four of the alleged victims' parents went to the police after hearing three of the children talk about the "nasty things" Martinez had done to them.

Investigators said the common thread between Martinez and his alleged victims is their membership in the Living Faith Christian Center in Oak Harbor, though it does not appear any of the assaults happened at the church.

"He had been inappropriately touching children - not at the church - but children of church members typically at their homes in a babysitting situation," Wallace said.

Police said Martinez detailed his crimes against the children in a taped interview, during which he said he "knew what he was doing was wrong" and therefore would apologize to the children afterwards. Martinez said he tried to stop several times but the temptations always returned, according to court documents.

Investigators said Martinez admitted to having been molested as a child for more than a decade.

Martinez is charged with 30 counts of sex crimes including child rape and child molestation. He's being held on $250,000 bail.

Police fear their may be other victims and are asking anyone with more information to come forward.