The couple suspected of killing 14 people at a Christmas party in California amassed thousands of rounds of ammunition and a dozen pipe bombs, authorities said.
Detectives released the information as they sought clues to the pair's motives and whether they had links to Islamist militants.
Syed Rizwan Farook, 28, and Tashfeen Malik, 27, his wife and mother of his 6-month-old daughter, were killed in a shootout with police five hours after Wednesday's massacre at the Inland Regional Center social services agency in the Californian city of San Bernardino.
Twenty-one people were wounded in the shooting, which ranks as the deadliest instance of U.S. gun violence in three years.
San Bernardino Police Chief Jarrod Burguan said at a news conference that the search of a townhouse leased by Farook and Malik in the nearby community of Redlands turned up flash drives, computers and cellphones.
They also found 4,500 rounds, 12 pipe bombs and bomb-making equipment.