A father fatally shot his twin 10-year-old children with a shotgun and then turned the gun on himself in a murder-suicide Monday in West Rogers Park on the North Side, authorities said.

Derrick Sanders, 45, was found dead at 11:04 a.m. in the hallway of a home in the 6200 block of North Richmond, according to Chicago police and the Cook County Medical Examiner’s Office. He had suffered a self-inflicted gunshot wound to his face.

Mason and Addison Sanders were found with gunshot wounds to the back of their heads, authorities said. Their deaths were ruled homicides following autopsies Tuesday.

Police said Sanders was the father of the two children. The children lived with their mother in the 4900 block of North Marine in Uptown, longtime neighbor Brenda Adams said. The couple had joint custody of the children, who would visit their father every other weekend.

Police spokesman Anthony Guglielmi called the crime “senseless.”

“Our condolences go out to the family affected by the senseless murder suicide at 6200 N. Richmond,” he tweeted. “A father, cowardly took the life of his two 10 year old children before turning the gun on himself. The offender had no previous history with the Chicago Police Department.”

Inside the building where Sanders lived, a pair of roller skates and two pairs of shoes sat on the floor outside the front door of his apartment Monday. Authorities had taped the door shut.

Leslie Lawrence, who lives in the unit directly below where the shooting occurred, was awakened at 5:15 a.m. by three loud shots. He said there was a long pause between each shot. He said he thinks the weapon was larger than a handgun, as he was able to feel the vibration from each shot while he was on his top bunk.

As someone who struggles with depression himself, Lawrence said he could see signs of depression in Sanders.

“I saw it in his face and his tone, so, me being friendly, I’d try to give him a couple of words, crack a joke,” Lawrence said.

However, Lawrence said he never expected Sanders to do anything like this. He said Sanders was protective of his children, even once yelling at Lawrence’s grandmother to quiet down so his daughter could sleep. He said he’d often see the family playing ball in the back.

Another neighbor, Iulia Oarca, had kind words to say about Sanders. A nanny, she was impressed that he took the time to play with his kids, and she said that he was well-mannered and considerate with neighbors.

Oarca was “shocked” that the same person who made sure she had enough room to park her car killed his children, and that it happened in her building.

“I’ve heard about robberies, but never anything that bad,” she said. “I can’t believe this happened here. This is not safe.”

Mourners began to decorate the gate outside the building where the shooting occurred Monday night, with flowers, balloons and votive candles. Among them was Adams, who helped put up a sign that said, “In memory of Addison and Mason.”

Adams described these kids as “happy, well-behaved children” who would often play with other neighborhood kids and her grandchildren. She, too, expressed confusion over Monday’s events.

“I don’t know why he did this,” she said. “I know he had some issues … but he loved his kids, it makes no sense.”