Gulzar Ahmad Malik spoke to The Associated Press by telephone from Jiddah, Saudi Arabia, saying he is "very, very sad.
"I am in such pain that I cannot even describe it," he said.
His daughter, Tashfeen Malik, and her husband, Syed Rizwan Farook, opened fire on Farook's co-workers a week ago in San Bernardino, California, killing 14 and injuring several others.
The couple later died in a gunbattle with police.
"Whatever God does only he knows better, and only God knows why did it happen," Gulzar Ahmad Malik said.
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The shooters radicalized at least two years ago and discussed jihad and martyrdom as early as 2013, FBI Director James Comey said today.
Tashfeen Malik, 29, held extremist views before she arrived in the US on a fiancee visa last year, he said.
Malik married Farook, an American citizen, in July 2014.
She was from Pakistan but traveled to Saudi Arabia, where her father has been a resident since the early 1980s, the Saudi Interior Ministry said.
A Pakistani counterterrorism official said the father works as an engineer, as do his two sons. The official spoke on condition of anonymity because he was not authorized to talk to the press.
Former classmate Afsheen Butt said Malik showed drastic changes after a trip to Saudi Arabia in late 2008 or early 2009.