Farook and Malik were in the final planning stages of an assault on a location or building that housed a lot more people than the Inland Regional Center, possibly a nearby school or college, according to federal sources familiar with the widening investigation.

Investigators have based that conclusion on evidence left behind on Farook and Malik’s computers and digital devices, not all of which the couple were able to destroy before they were killed in a firefight with police, the sources said.

Images of San Bernardino-area schools were found on a cellphone belonging to Farook, according to a law enforcement source. But the source cautioned that Farook may have had a legitimate reason to have the images because his work as a county health inspector involved checking on school dining facilities.

On Thursday, one of the federal government sources told The Times that Farook asked his friend and neighbor, Enrique Marquez, to buy two military-style rifles used in the attacks because he feared he “wouldn’t pass a background check” if he attempted to acquire the weapons on his own. The rifles were bought at a local gun store, the source said.