Dive team members were searching a small Southern California lake for evidence Thursday after learning that the couple who carried out a mass killing in San Bernardino may have been in the area on the day of the massacre.

The FBI sent a dive team to Seccombe Lake Park, about two miles north of the Inland Regional Center off South Waterman Avenue where 14 people were slain at a holiday party and four miles from where attackers Syed Rizwan Farook and Tashfeen Malik were killed in a shootout with law enforcement agents.

"We're seeking evidence of anything that had to do with this particular crime," said David Bowdich, assistant director of the FBI's Los Angeles office. "They were here at some point."

Bowdich said the search was expected to last days and there was no threat to the public.

Bowdich also revealed that a 22nd victim in the shooting had checked herself into the hospital with injuries she suffered in the attack. He offered no additional details.

Aerial video showed yellow police tape around a large part of the urban park and at least two dive team members in the water. It was not immediately clear whether any items were recovered.

Bowdich has said investigators suspect the couple made efforts to wipe their trail and get rid of digital and other evidence.

"We're just trying to ensure we account for every minute of the time," he said.

Farook, a coworker of those at the holiday party, and his wife stormed the IRC gathering Dec. 2 with semi-automatic rifles, fatally shooting 14 and injuring at least 20 others. Since the shooting, the FBI has interviewed hundreds of people and conducted searches in the area looking for evidence.

Malik moved from Pakistan to the U.S. in July 2014 and married Farook the following month. Farook was born in Chicago in 1987 and raised in southern California.

NBC News has reported the FBI is pursuing evidence Farook began formulating a terror attack more than three years ago but was spooked into lying low when the FBI announced that in nearby Chino it had arrested three individuals involved in an extremist conspiracy to travel to Afghanistan.

Special forces in Afghanistan captured a fourth individual, Sohiel Kabir, described as the recruiter. All four are now in prison.

"I'm not prepared to discuss that at this point because I just don't have all the answers," Bowdich told reporters at the lake.

Bowdich also declined to comment on Enrique Marquez, Farook's friend who bought the assault rifles used in the shooting and may or may not be in FBI custody.

FBI Director James Comey told the Senate Judiciary Committee on Wednesday that the two shooters were radicalized well before Malik came to the U.S. on a fiancee visa and had discussed jihad and martyrdom as early as 2013. The disclosure means Malik's radicalization had already begun when she applied for a visa to come to the U.S. to get married, and that the government's vetting process apparently failed to detect it.

Comey said he didn't know enough to say whether weaknesses in the visa process enabled Malik to enter the U.S.