Here is your shooter from yesterdays Massacre.

AN BERNARDINO, California (CNN) Mass shootings that involve multiple shooters are rare in American history: just two of the 28 deadliest shootings were carried out by more than one person.

The attack at the Inland Regional Center in San Bernardino, California, is now the third -- carried out by a man and a woman whose motives are still unclear.

Here is what we know about the attackers: Syed Rizwan Farook and Tashfeen Malik.

Police say Farook, 28, and Malik, 27, are either married or in a relationship. The Council on American Islamic Relations, a Muslimadvocacy group, said Farook has been married for two years -- but wouldn't confirm whether Malik was the wife's name.

They were not known to the FBI or on any list of potentially radicalized people, law enforcement officials said. Local authorities had said they did not know of any interactions the pair had previously with police.

Farook and his wife left their 6-month-old girl with Farook's grandmother Wednesday and said they had a doctor's appointment.

The grandmother became concerned when she saw reports of the shooting and couldn't reach him.

Farook, an American citizen, was an environmental health specialist with the San Bernardino County health department, which was hosting the holiday party at Inland Regional.

He had been there five years. Records list a man with his name and title who worked at the agency and made $53,000 in 2013.

He graduated from California State University San Bernardino with a degree in environmental health in 2009.

Farook was at the party but left abruptly before the shooting. He seemed angry, witnesses told police. He returned. And, along with Malik, he went into the building and began firing.

There are no indications his job was in jeopardy, police said. They're also unaware of any criminal history.

Farhan Khan, Farook's brother-in-law, told reporters he too was at a loss.

"I have no idea why he would he do something like this. I have absolutely no idea. I am in shock myself," Khan said.

He said the family, like the rest of America, will have to wait for the police investigation for answers.

Farook and Malik didn't appear to have left behind a note, a law enforcement official said.