The man and woman accused of opening fire at a holiday party in San Bernardino came prepared for a massacre.
The ATF said the suspects, who were killed in a shootout with police, were armed with four guns, an explosive device and several magazine of ammunition, NBC News reports. 
The suspects had two .223-caliber assault rifles and two semi-automatic handguns.
At least two of the four weapons were legally purchased, according to sources who spoke with NBC News.
“They were in tactical gear and had several mags full of ammunition fashioned to their body so they were ready for a gunfight should that occur,” ATF spokeswoman Meredith Davis said. “With my experiences with other mass shootings, there are indicators this was well-planned out and it was to be violent in nature.”