But the unassuming Bronx building supervisor also had a dark side, including a history of violence and mental problems.
His torment reached a peak last week when he grew so enraged that his 14-year-old daughter Ana was sending messages to a boy that he allegedly choked her and stuffed her body into a burning furnace boiler, police said.
The crime shocked friends and family - especially a cousin who received an ominous phone call from Matias in which he calmly described what he had just done.
"He called me, and said 'I have a problem. I killed Ana,"' Pablo Castillo said. "I couldn't believe what he said to me."
Castillo rushed over to the apartment, went down to the basement with police and saw a body in the boiler. "I looked for about a second and then I could not look anymore. I saw part of a burned body. I couldn't look any more. I couldn't believe it," he said, speaking in Spanish.
Police said Matias, 34, was being held at Bellevue Hospital Center and awaiting arraignment on charges of murder and manslaughter. The medical examiner's office is conducting tests to confirm that the body in the boiler was that of Ana and whether the teen was dead or alive before she was stuffed into it. It wasn't clear if he had an attorney.
Police Commissioner Raymond Kelly said last weekend that Matias called 911 and said he dumped her body in a wooded area in the Bronx. But when police searched the building Saturday, they discovered a body in the boiler.
The killing has raised questions about whether Matias should have had visitation rights for his children and whether he received the proper psychiatric care.
Matias had a history of emotional problems and was institutionalized after trying to set a car on fire with his children inside in Pennsylvania, police said. Family members said that it was only after one of his sons said goodbye to his sister that Matias changed his mind and decided not to torch the car.
It was not clear why he continued to have visitation rights after the car episode. Family members said that prior to Ana's death, Matias wanted to seek psychiatric help. They said he had applied for Medicaid insurance to cover the expense of counseling, but was denied.
His emotional problems apparently tore him and his wife Jocelyn apart several years ago, family members said. A few weeks ago, she had moved to Pennsylvania with Ana and her two younger brothers.
"He was a good father and she was a good daughter," said Matias' mother, Natalia Aquino, 50. She sobbed as she clenched a few crumpled tissues in her fists. "I don't know why he did that."
Family and friends described Ana as a vivacious and well-dressed 8th grader, who dreamed of becoming a model. Neighbors said Ana was her father's favorite child. He often gave her money to get her hair and nails done.
"She was always dancing and taking pictures," said Matias' 29-year-old sister, Casandra. "She always wanted to look cute."
Casandra said Matias never abused Ana. She claimed that the girl said that she wanted to stay with her father instead of moving to Pennsylvania. Her aunts believe Ana may have had boyfriend in the Bronx.
"She sounded happy," said her friend Trene Simmons, 11, who spoke to Ana about a week before the teenager's death. "She never mentioned something going on between her and her father."
Tenants in Matias' building said Matias was a quiet and courteous supervisor who was always ready to lend a hand when they had problems in their apartments. But "you never know when you can be talking to a demon," said Xiomare Cedeno, 49, who lives in the building.
Family members are also struggling to cope with the tragedy. "I have a photo of her that I keep looking at," said Castillo, the uncle who saw the burning body. "I can't eat, I can't sleep. All I think about is this event and wonder, how could it have happened?"
