Divers on Thursday explored a lake in San Bernardino, California, where the husband and wife who killed 14 people last week were reported to have been seen on the day of the shootings.
David Bowdich, the FBI's assistant chief for Los Angeles, would not discuss what evidence the divers were looking for, but one media report said there might be a computer hard drive in the lake.
Bowdich said the search of the lake could take several days. He said the FBI would be remiss not to follow up on every piece of information in the shootings.
Bowdich also said the number of wounded in the shootings rose to 22 Thursday when a victim discovered injuries related to the crime. He gave no details.
He said FBI investigators had met with the families and victims, adding that many may never recover from their physical and emotional scars.
Meanwhile, investigators were also intensely focusing on the activities of Enrique Marquez, who they said supplied the assault-style weapons to Syed Rizwan Farook and Tashfeen Malik, the couple who carried out the massacre and were killed in a police shootout.
Authorities said the friendship between Farook and Marquez goes back several years. The two liked to work on old cars, and Marquez converted to Islam and married a member of Farook's extended family.
Marquez, who has not been charged, checked himself into a mental health facility after the December 2 attack. Agents have searched his house, seized potential evidence and interviewed him repeatedly. Authorities said he has been cooperating.
The U.S. State Department is looking into whether it missed any signs of Malik's radical Islamist beliefs when U.S. officials in Pakistan scrutinized her request for a fiancee visa to come to the United States to marry Farook.
Authorities said no red flags turned up in their background checks on Malik. They said the questions focused on the legitimacy of her relationship with Farook and whether they planned to marry.
The State Department has defended its background check on Malik. But State Department spokesman John Kirby told CNN Thursday, "Every now and then, someone's going to get through. We don't like that, but that's the reality."
After a closed-door briefing on the investigation Thursday, U.S. Representative Matt Salmon, an Arizona Republican, denounced the State Department review of Malik.
"They say the system has all these fail-safes," Salmon said. "Apparently, there aren't enough fail-safes. This woman was obviously radicalized years ago, and she got through the system."