(CNN) -- A 14-year-old California boy told police he drowned his 4-year-old neighbor on Friday because the child had threatened to tell his mother the older boy had molested him, according to an affidavit made public Wednesday.

Raul Renato Castro has been charged in Fresno County as an adult, with special circumstances including murder during a child molestation, sodomy, kidnapping and murder of a witness to prevent testimony, according to the district attorney's office.

He faces separate felony charges of kidnapping, sodomy and child molestation.

The affidavit, filed by the Fresno County Sheriff's Department, says Castro told investigators he lured the victim, Alex Christopher Mercato, into his apartment "by telling the victim he had something to show him."

Police have said no one else was in the Mendota, California, house at the time.

Castro then talked the boy into entering the bathroom, according to the document. Castro said he then sodomized the child, after which "the victim tripped over the carpet, fell, and hit the back of his head on the bathtub," the affidavit says.

"Castro said the victim started crying and told Castro he was going to tell his mother. Castro said he panicked and decided to kill the victim by drowning him in the bathtub.

"Castro turned on the water to the bathtub and filled it up just enough to put the victim's face underwater and drowned him. Castro said he held the victim underwater 2-4 minutes. Castro got into the bathtub with the victim, held him down until the victim died."

"Castro then carried the victim over his left shoulder and put him [in]... the clothes dryer to conceal him."

The incident occurred Friday afternoon, after Mercato's parents discovered that their child, who had been playing outside their house, was missing, Fresno County Sheriff Margaret Mims told reporters Monday.

The parents called police, who searched the neighborhood and nearby parks in Mendota, 33 miles west of Fresno, she said. Soon, the FBI was called in.

On Saturday, authorities resumed the search and found the body stuffed inside the dryer in the apartment next door.

An autopsy determined the victim had drowned.

Under California law, a 14-year-old is not eligible for the death penalty or a sentence of life without the possibility of parole. If found guilty, Castro could receive no more than 32 years to life plus 15 years.