A California fire captain accused of killing his girlfriend and her young son — and attempting to kill another child — entered not guilty pleas in court on Monday.

Darin McFarlin, 47, is on unpaid administrative leave from CalFire, KXTV reported, after his arrest last week for the murders of 29-year-old old Marissa Herzog (previously identified as Marissa Divodi-Lessa) and her son Josiah, a second grader.

He stands charged with two counts of first degree murder, one count of attempted murder, and domestic violence and child abuse charges.

Court documents say the murders took place to prevent the victims’ testimony for a crime, but they do not specifically reveal what that crime was. They do, however, detail what investigators think happened on the evening of August 21.

According to the Sacramento Bee, prosecutors say that McFarlin attacked Herzog inside a “bedroom before she left the room and used her cellphone and before he obtained the gun and went out to the dining room to kill her.” The document says that Herzog’s murder was “willful, deliberate and premeditated” and that she was killed because she witnessed a crime, the Mountain Democrat reports.

The boy was also killed because he witnessed a crime, the newspaper said.

McFarlin then attempted to kill a second child, later identified by Herzog’s family as her daughter. The court documents say the killer “did willfully and unlawfully, inflict unjustifiable mental suffering on a child or permit a child to suffer unjustifiable mental suffering under circumstances and conditions likely to produce great bodily harm.”

El Dorado County deputies found Herzog dead at the scene when they arrived, as CrimeOnline reported. The boy was taken to a hospital, where he died. McFarlin had fled the scene and was later arrested several counties away in Mono County.

The El Dorado County District Attorney’s Office added special circumstances to the murder charges — committing multiple murders, murder of a witness to prevent testimony, and intentional discharge of a firearm causing death and child endangerment — making McFarlin eligible for the death penalty if he’s convicted, the Bee reported.

McFarlin is being held without bail and has a preliminary hearing set for September 29.