(AP) -- Syed Farook was known to pray every day at his mosque, and he impressed brothers Nizaam and Rahemaan Ali by memorizing the Quran. He talked of getting a master's degree, was fond of tinkering with cars and proudly announced when he was married.

The last time Rahemaan Ali saw their friend was three weeks ago, when Farook abruptly stopped going to the mosque where they all worshipped, Dar Al Uloom Al Islamiyah in San Bernardino.

"He never, ever talked about killing people or discussed politics, or said that he had problems at work," Rahemaan Ali said.

Their description of a man in a sweet-spot of life, devoted to his family and religion with a good job, clashed with the suspect who along with his wife, police say, staged an commando-style attack at a work holiday party at a social service center on Wednesday.

A day after the rampage that left 14 dead, details about Farook's life began to take shape, but critical questions went unanswered, including how he and his wife, Tashfeen Malik, quietly and methodically stockpiled arms and explosives for the attack.

The details come as authorities try to determine what could have motivated the attack, which injured more than a dozen others.

The FBI was investigating the shootings as a potential act of terrorism but had reached no firm conclusions, said a U.S. official briefed on the probe who spoke on condition of anonymity because the person was not authorized to discuss the ongoing investigation.

Police said the couple had more than 1,600 bullets when they were killed by authorities, and that the shooters had more than 3,000 rounds of ammunition at their home, as well as 12 pipe bombs and tools that could be used to make explosive devices.

The attack came as a shock to leaders in the Muslim community, and many wondered what could have motivated it.

"We don't know the motives. Is it work, rage-related? Is it mental illness? Is it extreme ideology? At this point, it's really unknown to us," said Hussam Ayloush, executive director of the Council on American-Islamic Relations, based on conversations with Farook's brother-in-law.

Syed Rizwan Farook was born in Chicago on June 14, 1987, to parents born in Pakistan. He was raised in Southern California.

In July 2010, he was hired as a seasonal public employee and served until December of that year, according to a work history supplied by San Bernardino County. In January 2012, he was rehired as a trainee environmental health specialist before being promoted two years later.

The Ali brothers said he was always tinkering on his cars and rebuilding engines. They remember him driving a newer-model Mustang and an older Lexus at various points.

Rahemaan Ali said Farook seemed happy and his usual self when he saw him, and both brothers said they never saw anything in Farook that would lead them to think he would ever commit violence.

"I can't believe it. There's no way to express the shock I'm in," said Nizaam Ali. "This was a person who was successful, who had a good job, a good income, a wife and a family. What was he missing in his life?"

They remember when Farook announced that he would be getting married, saying he had met his future wife online and that she was Pakistani. Farook told the brothers that he traveled to Mecca in Saudi Arabia last summer.

They said he was only gone for three weeks to a month before returning to the U.S. with his wife.

Malik never came through Saudi Arabia and instead traveled through Islamabad, arriving on a K-1 visa for fiancées and with a Pakistani passport. The couple had a 6-month-old daughter, who they left with relatives before heading to the center.

His job at the county Department of Public Health took him Wednesday to the Inland Regional Center, where the department held a holiday banquet, Ayloush said. Co-workers described him as aloof while others said he could be chatty when the subject interested him.

Patrick Baccari, who sat at the same table as Farook at the party, recalled he was short on words and inclined to talk about cars, not religion. "It seems the only response I ever got from him was if I initiated the conversation," Baccari said.

A friend of a man killed in the rampage said he and Farook had a heated conversation about Islam two weeks before the attack.

Kuuleme Stephens said she once happened to call Nicholas Thalasinos, a Messianic Jew who was passionate about pro-Israel causes, while he was at work and having a discussion with Farook.

Thalasinos, 52, identified Farook by name and told her that he "doesn't agree that Islam is not a peaceful religion," Stephens said.

Stephens said Farook replied that Americans don't understand Islam. According to Stephens, both men worked as restaurant inspectors and regularly discussed politics and religion. She added that Thalasinos did not think their conversations would turn violent.

Thalasinos' wife, Jennifer Thalasinos, told The New York Times that her husband had talked about Farook but never said anything negative.

Little is known about Farook's upbringing, though he grew up in a family in which his mother accused his father of being an abusive alcoholic.

Farook's mother alleged in 2006 that her husband, also named Syed, attacked her while her children were present, dropped a TV on her and pushed her toward a car, according to divorce records.

Rafia Sultana Farook filed a petition for a domestic violence order of protection on July 3, 2006, against her husband, also named Syed.

Rafia Farook said she was forced to move out of her home with three of her children because her husband continually harassed her "verbally and physically and refused to leave the home," according to the divorce records.

The Associated Press could not immediately reach the father for comment. No one answered the door at a home in Corona where a neighbor said the father lived. The AP was unable to corroborate the allegations in the records.

Dane Adams, of Corona, said Syed Farook's father, who moved in with his son, the younger Farook's brother, two doors down a few months ago, was talkative, often visiting as Adams worked on classic cars in the garage. He talked about his family and said he was divorced.

Adams said he often saw the man walking with his grandchild, who Adams guessed was about a year old.

"That baby's got the cutest smile in the world," he said.

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Tucker reported from Washington, D.C. Associated Press writers Holbrook Mohr in Jackson, Mississippi, Gillian Flaccus in Anaheim, California, Amanda Lee Myers in San Bernardino, California, Garance Burke in San Francisco and Jason Keyser in Chicago also contributed to this report.