WASHINGTON (AP) – Two law enforcement officials say a bomb left behind by the couple responsible for the December attack in San Bernardino, California, failed because it was poorly constructed.

One official says 28-year-old Syed Rizwan Farook and 29-year-old Tashfeen Malik drove around San Bernardino after the shootings at the social services center. They stayed close to the site of the shooting, apparently trying to detonate the remote-controlled bomb.

The officials were briefed on the investigation and spoke on condition of anonymity because they weren’t authorized to discuss the case publicly. The attack left 14 people dead.

One official says the couple’s two cellphones were so badly crushed that investigators haven’t been able to conduct a forensic examination. Their computer hard drive hasn’t been found.