Police say they also recovered bomb-making material and yet more ammunition at the couple's home.
Authorities are also looking to determine if the pair had links to Islamic militant groups abroad.
Police in the United States have identified the dead attackers in the California shooting as 28 year-old Syed Rizwan Farook and his wife, 27 year-old Tashfeen Malik.
Authorities in San Bernadino are trying to discover why a married couple with a baby daughter carried out one of the worst gun attacks in the US in recent years.
The couple were found in their car with thousands of rounds of ammunition after a shootout with police.
Police chief Jarrod Burguan says a search at the couple's home also found more ammunition and evidence of other material that could be used to create bombs.
"I will confirm that the search that took place revealed that there were 12 pipe bomb type devices in that house or in the garage of that house. There were also hundreds of tools many of which could be used to construct IED's or pipe bombs. And in addition to that they had other material to produce some additional bombs as well. There were another 2,000 nine millimetre rounds found at that house. Over 2,500 .223 rounds that were found, and there were additional several long rifle rounds that were found there."
Authorities say so far there is no evidence of a direct connection between the shooters and any militant group in the US or abroad.
Hussam Ayloush, who heads the Los Angeles area chapter of the Muslim advocacy group Council on American-Islamic Relations says Mr Farook, a US-born citizen, was the son of Pakistani immigrants.
Ms Malik, his wife, was born in Pakistan and had been living in Saudi Arabia before marrying Mr Farook.
Police say Mr Farook had no known criminal record yet the equipment found indicated there was some degree of planning behind the attack.
FBI spokesman David Bowditch says the couple's international connections are being investigated.
"It appears that he came back into the US in July 2014 as I said earlier. I do not know all the countries he visited. We know he did go to Pakistan at one point. We know she is here on a K1 visa under a Pakistani passport."
United President Barack Obama says investigators do not yet know why the two suspects carried out the mass shooting but he's vowed agencies will find it out.
After meeting national security advisers, Mr Obama expressed sympathy for the victims but renewed his call for greater gun control.
He says the United States needs to pass laws to make it harder for people to get access to weapons when they're seeking to do harm.
"We all have a part to play. And I do think that as the investigation moves forward it's going to be important for all of us, including our legislatures, to see what we can do to make sure that when individuals decide that they want to do somebody harm or make it a little harder for them to do it. Because right now it's just too easy. And you know what we're going to have to I think search ourselves as a society to to make sure that we can take basic steps that would make it harder not impossible but harder for individuals to get access to weapons."
Crowd-sourced website shootingtracker.com keeps a running tally of US gun violence.
It says there have been more than 350 shootings this year in which four or more people were wounded or killed in the United States.
