On Wednesday, a couple entered the Inland Regional Center in San Bernardino and opened fire on a gathering of county employees who were celebrating the holiday season. The attack left 14 victims dead and 21 others injured.
The alleged gunmen, husband and wife, Syed Rizwan Farook and Tashfeen Malik, were armed with two assault-style weapons and two handguns, according to authorities.
Following a car chase and a shootout in the middle of the street, the couple was killed by police. Investigators are still tracking down the origin of the weapons they used in the attack and additional firearms and explosives found in their home. Here’s what we know so far:
The suspected shooters wore "tactical-style" vests as they allegedly fired their rifles into the conference room of 75-80 unsuspecting people, according to San Bernardino Chief of Police Jarrod Burguan.
They unsuccessfully tried to convert one of the rifles used in the attack from semi-automatic to fully automatic, according to a law enforcement official briefed on the case.
All four guns were purchased legally, according to law enforcement. Both pistols were purchased by Syed at Annie's Get Your Gun in Corona, CA in 2011 and 2012, authorities said.
At the gun store, a woman told ABC News she was “sickened” by what happened, but would not provide further comment. However, law enforcement sources confirmed the location.
The two long guns were purchased by another individual. FBI Director James Comey said that the identity of the purchaser is known to the FBI and that the person is not a "not a suspect, at least at this point, in this matter.”
At the initial shooting in the Inland Regional Center, the couple fired between 65 and 75 rounds.
"They sprayed the room with bullets," Burguan said.
Four .223 rifle magazines were dropped by the suspects and left at the scene of the attack and later recovered as evidence.
Inside and around the rental car that was the scene of their final shootout, police found over 1,400 rounds for the rifles and over 200 9 mm rounds for handguns, according to Burguan.
More than 3,000 rounds of ammo were found at the alleged attackers home. The ammunition included, 2,000 9 mm rounds, 2,500 .223 caliber rounds and additional “several hundred” .22 long rifle rounds, much smaller rifle round often used for target practice.
During the final shootout with police, the suspects are believed to have fired about 76 rifle rounds at the officers at the end of their pursuit. Twenty-three officers on the scene fired approximately 380 rounds at the suspects, killing them both. Two officers were injured during the shootout.
Explosive devices were found at the initial scene of the attack and additional explosives and tools were found by police at the home of the suspects.
Three pipe bombs combined together were found attached to a "remote control car" at the center where county employees where holding their event. The device appeared not to have worked, according to investigators. It was later disposed of by the bomb squad.
The device was described by one source as “rudimentary.”
Twelve pipe bombs and hundreds of tools that could be used to make explosives were later found in their house.
The galvanized pipe used in the bomb construction was shaped like an elbow and had metal endcaps. Sources say the explosive filler was likely black powder or smokeless powder, commonly known as gunpowder.
The FBI said that they are “looking into” any similarities between the IED’s found on the scene and those described in instructions published in Inspire Magazine, the online publication of al Qaeda in the Arabian Peninsula.
Some of those designs were employed by the Boston marathon bombers.
Pierre Thomas, Josh Margolin, Mike Levine and David Herndon contributed to this report.