After more than eight hours of no activity, officers entered the residence and discovered the man dead on the second floor.
At an 8 p.m. news conference, LAPD Deputy Chief Kirk Albanese said a coroner's investigation would determine the cause of the suspect's death.
The suspect's identity could not be confirmed. An approximate time of death was not yet known.
A high-powered rifle was found near the suspect.
Albanese said a coroner's investigation would determine the cause of the suspect's death. A criminal investigation was also in progress because the suspect fired on police. An administrative investigation was also to be launched because police used deadly force.
Albanese said police tried to communicate with the suspect over a public-address system since they could not make contact otherwise. The suspect never spoke to police, according to Albanese.
Authorities said police officers were called to the area for a domestic dispute at about 10:38 p.m. Sunday. Officers responding to the call found a woman with cuts and bruises. The man pulled out a gun at the scene.
The suspect refused to follow police commands to come out of the home for several hours, and instead engaged in gunfire with officers, police said.
"We heard gunshots right away. We heard two gunshots," said Brenda Soriano, who lives next door to the residence. She was one of the neighbors evacuated to Sylmar High School during the ongoing standoff.
"[Officers] finally broke in and one of the cops was shot in the face. He ran out yelling that he was shot in the face," said Soriano.
The officer, identified as Steve Jenkins, was shot while officers were responding to a domestic-dispute incident in a gated community near Dronfield Avenue and Bledsoe Street at about 2:15 a.m.
Jenkins was taken to Providence Holy Cross Medical Center in Mission Hills, where he was in critical but stable condition Monday.
Officials said the suspect's wife suffered moderate injuries.
A neighbor said the suspect is about 50 years old and lives in the residence with his wife.
Police believe the suspect may have had several weapons.
Latest on Sylmar standoff
The standoff had been going at a Sylmar home for more than 16 hours. There were dozens of LAPD officers and L.A. County Sheriff's deputies on scene Monday.
The LAPD used what is known as a "BatCat," a large crane-like robotic tractor with a mounted camera, to clear a path into the residence in case officers need to move in.
"It's able to grab and maneuver items," said Neiman. "By the same token it can actually puncture through locations and remove the debris. That's how the holes were breached in this case."
Just before 11 a.m., police fired tear gas into the home. The suspect started shooting at officers from a window, and they returned fire.
"He fired a weapon at the officers," said Neiman. "Unknown what type of weapon. Our officers did return fire and at this point it's unknown what the suspect's condition is."
After more than eight hours of no activity, police entered the residence and discovered the man's body on the second floor.
Latest on officer's condition
Doctors say Jenkins is in critical but stable condition. He is on a breathing tube and is currently sedated.
Jenkins was shot twice. One bullet hit him in the cheek and exited through his jaw. The second bullet hit Jenkins near his collarbone and exited the left side of his chest.
Doctors said the wound to his jaw is going to require future operations.
"That injury resulted in multiple rib fractures, some damage to large blood vessels, damage to his lung and quite a bit of blood in his chest," said trauma surgeon Dr. Bradley Roth. "The patient is sedated, he is on a breathing machine. He has two chest tubes in his left chest and he is more or less stable at this time. He is critically ill but stable."
Fellow officers, including his partner, have donated blood for him. Doctors said Jenkins faces several more surgeries for his injuries, including reconstructive surgery on his jaw. The blood drive at the hospital was so successful the hospital planned to do it again Tuesday.
According to doctors, Jenkins is expected to recover.
Jenkins is a 22-year LAPD veteran and works in the Metropolitan Division as a K-9 handler.
His wife, who is a sergeant at the LAPD's 77th Division, was flown to Providence Holy Cross Medical Center in an LAPD helicopter. Their son Andrew is also an LAPD officer, and both have been by his side at the hospital.
"He has been a canine handler for many years, very well respected. Part of one of the most well-known and highly-regarded divisions of the Los Angeles Police Department Metropolitan Division," said LAPD Chief Charlie Beck.