The investigation of the California shooting case has taken the Federal Bureau of Investigation (FBI) to the Seccombe Lake in San Bernardino, California, where a search for evidence is taking place.

Divers are searching the waters for new evidence, which according to CNN is a "hard drive that belonged to the couple."

David Bowdich, assistant director of the FBI field office in Los Angeles, said that an unspecified lead led them to the lake, where the couple Syed Rizwan Farook and his wife Tashfeen Malik, was suspected to be around on the day of the killings.

Bowdich told Reuters that he would not disclose the "specific evidence we're looking for."

The lake is only 4 km from the Inland Regional Center where the couple had opened fire killing 14 and injuring 22.

The FBI is treating the case as a terrorist attack as the couple is said to have declared affiliation to Isis. Also a repository of arms and ammunition was found in their home.

Their earlier investigations also revealed that the couple was radicalised before they started dating online.

The couple had been discussing martyrdom and jihad online since 2013, before they met, informed FBI Director James Comey to a US Senate on Wednesday.

Conflicting reports from government sources have come forth in the case as some say that Malik tried to contact multiple Islamist groups, who probably ignored her attempts fearing a 'sting operation', while others have said that no link to any Islamic group have been found. 

"The current impression is that these two people were acting alone," US Senator Angus King of Maine told CNN after a meeting with US Homeland Security Secretary Jeh Johnson and John Mulligan, Deputy Director of the National Counterterrorism Center. 

Republican member of the House Intelligence Committee Peter King asked for "more surveillance in the Muslim community here in the United States" after the session.

"You look where the terror is going to come from, and right now, it is going to come from the Muslim community. It's a small percentage, but to me, the only way you find out about it in advance is having sources and informers on the ground, having constant surveillance," he added.