The South Pasadena man accused of killing his 5-year-old son is expected to plead guilty Tuesday.

Aramazd Andressian Sr. will admit to the killing when he returns to Alhambra Superior Court for a hearing, KABC Channel 7 has reported. He is expected to face a sentence of 25 years to life in prison.

According to documents obtained by this news group, Andressian Sr. likely had few other options than to admit his guilt. A Los Angeles County Department of Children and Family Services report showed Andressian Sr. in late June revealed to investigators he harmed the boy and left him in Santa Barbara County, then later told them where to find the body.

Copies of the July 3 DCFS report show a “reporting party” — whose identity was redacted from the document — relayed to county officials what Andressian Sr. told sheriff’s detectives about the day the boy went missing.

The report was filed three days after the body of the boy, Aramazd Andressian Jr., was found near Lake Cachuma.

• Photos: The search for Aramazd “Piqui” Andressian Jr.

According to the report, Andressian Sr. told sheriff’s investigators where the body was located in the days surrounding his arrest in Las Vegas on June 23 and his extradition back to Southern California on June 30. The report shows he also told the investigators he had “harmed” the boy and “left him.”

All the names in the heavily redacted documents — supplied to this publication after requesting copies of reports on Andressian Jr. — were blacked out.

Under Senate Bill 39, juvenile case files pertaining to a child who died as the result of child abuse or neglect must be released to the public, with limitations.

The specifics included in the DCFS reports match up with the incidents surrounding the disappearance of the boy and the discovery of his body.

Attorney Ambrosio Rodriguez, who is representing Andressian Sr. in the criminal case, said he had not seen the DCFS reports.

The law enforcement-penned reports in the case have been sealed by the court, Rodriguez said. He declined to discuss the allegations against his client, citing the court order sealing the documents.

A spokeswoman for the Los Angeles County District Attorney’s Office on Monday declined comment about the DCFS reports.

The sheriff’s homicide lieutenant on the case couldn’t be reached for comment Monday morning.

The county prosecutors last month charged Andressian Sr. with murder in the April 21 death of his son. The mother, Ana Estevez, reported the boy missing April 22, when Andressian Sr. failed to show for a child custody exchange that day.

• Related story: Social worker, police visited troubled family

The father was found unconscious outside his parked car at Arroyo Park in South Pasadena the morning of April 22. There was no sign of his son.

Detectives found the interior of the car soaked in gasoline. Inside the car were matches and a gas can. There was also a rag in the gas tank.

A search for the boy began immediately after but dragged on for more than two months.

Following Andressian Sr.’s arrest, a search was conducted based on what he was said to have told investigators. The remains were found June 30 in a wooded area in San Ynez.

The specific area where the father allegedly left the child is blacked out in the July 3 DCFS report.

The July 3 report also reveals additional details about where Andressian Sr. told investigators he went with his son in the hours before the boy was reported missing. The report shows Andressian Sr. told authorities who found him unconscious near his car in Arroyo Seco Park that he had driven to Lake Cachuma the day before, then left around 10 p.m. He told investigators his son wanted to go miniature golfing before his April 22 speech therapy in San Marino.

Andressian Sr. said he drove from Lake Cachuma to the Arroyo Seco miniature golf course. He arrived around 4 a.m., but it was closed.

He told the deputies after that the boy fell asleep in the back seat. Andressian Sr. then said he took five Ambien pills and drank cough syrup. He remembered nothing after that.

Another report from April 24 provided to this publication shows a caller told DCFS that a car seat was found in Andressian’s vehicle but that the boy was nowhere to be found. The caller told DCFS it was unclear if the boy got out of the car himself, if someone had kidnapped him or if the father was withholding information. The caller said there was no evidence suggesting Andressian Sr. had been attacked.

The July 3 DCFS report mentions that the body discovered June 30 was still being identified by the coroner and that a cause of death had not been determined. Authorities highly suspected the remains are of the missing boy.

The same report listed the father as the alleged perpetrator of the physical abuse and severe neglect.

While the DCFS reports blacked out the name of the parties who kicked off the investigations, one came in by email and another by phone. Both sources were mandated reporters, which means someone whose profession the law requires to report suspected child abuse.

The funeral for Aramazd “Piqui” Andressian Jr. was held July 18.

Staff writer Brian Day contributed to this report.