A 66-year-old substitute school custodian was charged Thursday with sexually assaulting a 13-year-old boy.

Four felony counts of first-degree criminal sexual conduct have been filed against Marvin Allan Sipes of Mankato, a retired Mankato School District custodian who had been filling in as a substitute.

The charges stem from four different incidents that allegedly took place at Sipes’ mobile home in the 300 block of Southhaven Drive, the boy’s residence and at a location in rural Blue Earth County between June and September, the criminal complaint said.

Sipes’ neighbors said several plain-clothes police officers pulled up to his residence Tuesday afternoon and arrested him at gunpoint before spending several hours searching the mobile home. Sipes has been in jail since the arrest undergoing questioning. Neighbors described Sipes as a quiet man with roommates who hadn’t been seen at the residence since his arrest.