Federal authorities have compiled a detailed timeline surrounding the terror attack in San Bernardino that killed 14 people. But they asked for the public's help Tuesday to fill in an 18-minute gap in the whereabouts of the husband-and-wife killers.

David Bowdich, the assistant director in charge of the FBI's Los Angeles office, said investigators so far have found no evidence there were any targets other than the Inland Regional Center, where Syed Rizwan Farook, 28, and Tashfeen Malik, 29, opened fire on a holiday luncheon gathering of Farook's co-workers in the county health agency.

Mr. Bowdich also reiterated that there's no evidence the attack was directed from overseas, but he said nothing has been ruled out.

While much has been learned in the five weeks since the Dec. 2 massacre, he said investigators still need information about a gap in the timeline between the attack and the pursuit and shootout in which both attackers were killed.

Bowdich said investigators hope to find out if the assailants contacted anyone or stopped anywhere between 12:59 p.m. and 1:17 p.m. that day. The rest of their movements through the adjacent cities of San Bernardino and Redlands in a rented black Ford Expedition have been tracked, he said.

"It's possible that they stopped, whether it be a storage area, a residence, a business. It's possible there was a contact made. We just don't know," Bowdich told reporters. "''It very well may not be an important fact, but until we close that gap we just don't know for sure."

He urged people to call if they have any information.

Federal authorities have said Mr. Farook, a restaurant inspector, and his wife, who came to the US from Pakistan in July 2014 so she could marry him, were radicalized Muslims long before the attack but never drew the attention of law enforcement.

They amassed ammunition and explosives at their home, and on Dec. 2 donned black commando outfits and face masks and launched their attack. Immediately afterward a post on a Facebook page associated with Malik said the couple pledged allegiance to the leader of Islamic State, according to federal authorities.

After the rampage, the couple visited an area lake at 11:45 a.m. and then appeared to zig-zag throughout the area, stopping at certain places, Bowdich said.

"There's no rhyme or reason that we can make for it yet, however, again, that 18 minutes is critical," Bowdich said.

Bowdich said authorities have carried out 29 search warrants, conducted 550 interviews and scoured social media to piece together a timeline of the couple's whereabouts after the attack.

Get the Monitor Stories you care about delivered to your inbox. By signing up, you agree to our Privacy Policy

The only person charged in connection with the attacks is Enrique Marquez Jr., a friend of Farook's accused of providing the assault rifles used in the massacre. He is scheduled to be arraigned Wednesday in federal court in nearby Riverside.

A grand jury last month indicted Mr. Marquez, who grew up next door to Farook, on charges that include making false statements about when he bought the weapons and conspiring with Farook on a pair of previously planned attacks that were never carried out.