Police served a search warrant on a home in Nanakuli early today and arrested a 56-year-old man on multiple sexual assault charges.

Henry Moisa was charged with four counts of first-degree sexual assault and one count of promotion of pornography to a minor. Bail was set at $250,000.

The charges against Moisa involve a 15-year-old boy, police said.

The investigation was launched following a tip from the boy's family, police said.

They said the investigation is ongoing and that there may be additional victims.

At a news conference this afternoon, police said officers executed the warrant at 4:10 a.m. at Moisa's house, 87-2148 Farrington Highway, and found a number of still images of male juveniles. No videos were found, police said.

None of the photos had names.

Police said the 15-year-old was an employee of Moisa, owner of A's Party Portable Toilet Rental. Police said Moise employed several juveniles.

Police said four incidents occurred between May 31, 2007, to May 5, 2008, leading to the four sexual-assault charges.

Moisa is being held in lieu of $250,000 bail, police said.

Anyone with information to share is asked to call the Honolulu Police Department's criminal investigation Division at 529-3115.