Syed Rizwan Farook with his wife Tashfeen Malik (Associated Press Photo)
A homemade bomb left behind by the husband and wife who perpetrated a mass shooting in San Bernardino, California, in December failed to detonate because it was poorly constructed, two law enforcement officials told The Associated Press.
The failure compelled Syed Rizwan Farook, 28, and Tashfeen Malik, 29, to drive around the area after the shootings that killed 14 people. They were apparently trying to set off the remote-controlled bomb, one of the officials said.
The officials were briefed on the investigation and spoke on condition of anonymity because they weren't authorized to discuss the case publicly.
Investigators believe the couple intended to detonate the improvised explosive device - placed in a bag at the scene of the shooting that morning by Farook - to kill emergency responders or possibly before their attack.
The plan to set off an explosive device is similar to an aborted 2012 plan by Farook and his longtime friend Enrique Marquez, who has been charged for his role in aiding the violence. The pair planned to explode pipe bombs on a freeway and then shoot emergency responders.
The device found at the scene in San Bernardino consisted of three pipe bombs, constructed with Christmas tree lights and attached to a remote-control toy car switched to "on." The couple had the remote with them in their rented SUV. It was found after the shootout.
The FBI is still trying to determine where the couple was and what they did during 18 minutes between the December 2 attack and a shootout with authorities that left them dead.
Investigators have no details on the couple's whereabouts between 12:59 pm and 1:17 pm that day and worry that they may have met with someone, dropped by a storage unit or visited a residence.
One of the officials said a hard drive has still not been found, and two cellphones, which were sent to the FBI lab, were so badly crushed that investigators have not yet been able to conduct a forensic examination on them.
The errors constructing the explosive device may indicate that the two killers were self-taught, but without potential electronic evidence on the couple's computer hard drive and phones, it is hard to know for sure, officials said.
The FBI has said there's no evidence that the attack was directed from overseas.