Updated

Six weeks after the San Bernardino terror attack, the FBI official leading the investigation says some of the most basic questions remain the most elusive to answer.

David Bowdich, chief of the FBI's Los Angeles field office, said Friday that those questions include whether anyone else was involved in the Dec. 2 massacre and whether more violence was planned.

Bowdich says another key question was why the shooters, Syed Farook and his wife, chose the time and place of the attack. Bowdich says the FBI also is still trying to fill an 18-minute gap in the whereabouts of the husband-and-wife killers following the shooting.

Bowdich says he and San Bernardino officials met with about 130 victim family members and survivors of the attack Thursday to try to answer their questions.