In a letter to Attorney General Loretta Lynch, Homeland Security Committee Chairman Ron Johnson asked her agency to furnish the requested evidence, along with answers to more than a dozen questions he posed about the investigation, by Dec. 24.
A Justice Department spokesman declined comment, except to say, “We have received the letter and will review it.”
The 10-page letter gives no explicit rationale for the request other than to cite the committee’s congressional oversight authority in matters of national security.
But the nature of Johnson’s queries and scope of the evidence he asked to review indicated his committee was looking for possible intelligence lapses in tracking Islamic extremist activity that might have worked to the killers’ benefit.
“What did you miss and how can we tighten that up,” a source close to the senator told Reuters in characterizing the thrust of Johnson’s inquiry.
Among the materials Johnson requested are any communications unearthed by investigators pointing to the couple’s plans for the massacre, how they concealed their intentions from law enforcement and any other attacks they might have contemplated.
He also asked for information the department had obtained that would suggest any sponsorship of the couple by “a foreign terrorist organization.”
U.S. officials have said their investigation has yet to turn up any evidence that Syed Rizwan Farook, 28, or his wife, Tashfeen Malik, 29, were directed by foreign militants when they stormed a holiday gathering of his co-workers on Dec. 2 and opened fire with assault rifles.
Fourteen people died and 22 others were injured in the rampage, which the Federal Bureau of Investigation said it is treating as an act of terrorism inspired by Islamic extremism, the most lethal such attack on U.S. soil since Sept. 11, 2001.
Farook, the U.S.-born son of Pakistani immigrants, and Malik, a Pakistani native he married last year in Saudi Arabia, were killed in a shootout with police hours after their assault in San Bernardino, 60 miles (100 km) east of Los Angeles.
The Senate inquiry came about as new Gallup poll released on Friday showed Americans losing faith in their government’s ability to protect them from militant attacks, while a suspicious fire at a Southern California mosque raised new concerns about an anti-Islamic backlash.
The fire, which erupted in the lobby of the Islamic Society of Coachella Valley, 75 miles (120 km) east of San Bernardino, caused smoke damage but no injuries, though the Riverside County Sheriff’s Department called the blaze a possible arson.
Last week’s deadly mass shooting has sparked intense debate about how Farook and Malik managed to avoid detection by law enforcement as they planned their attack while amassing a large arsenal of weapons, ammunition and explosives.
FBI officials have said the couple were not under investigation at the time of their attack.
But federal agents have since learned that the couple had been steeped in radical Islamic ideology for some time, and were discussing jihad and martyrdom online with each other as far back as 2013, a year before they met in person, FBI Director James Comey told the Senate Judiciary Committee on Wednesday.
While the couple is known to have declared they were acting on behalf of the Islamic State, there was no evidence that the militant group controlling vast swaths of Iraq and Syria were even aware of them prior to their attack, Comey said.
Investigators believe Malik had tried contacting a number of militant groups overseas in the months before the massacre but was ignored, according to U.S. officials.
Neither Johnson nor other lawmakers briefed on the case on Thursday publicly expressed a lack of confidence in the investigation. But some questioned whether in hindsight some warning signs might have been overlooked and whether current surveillance of potential extremists is sufficiently robust.
That sentiment came through in questions posed by Johnson’s letter. In one, he asked whether Farook, Malik or Enrique Marquez – a former Farook neighbor who bought the rifles used in the mass shooting – had ever “been under any investigation or surveillance by U.S. law enforcement or counter-terrorism officials? Please explain.”
He also asked which U.S. agencies knew of Malik’s alleged connections to a radical cleric at a mosque in Islamabad, Pakistan, and requested information about U.S. security checks conducted on the couple when Malik applied for a visa to enter the United States as Farook’s fiancée.
Some lawmakers have said Malik used a fake address on her application that went undetected.
“What, if any, further indicators of threats to national security were missed by the queries of Mr. Farook and Ms. Malik?” the letter asks.