AP sources: Bomb in San Bernardino attack was poorly built

WASHINGTON (AP) — A homemade bomb left behind by the husband and wife who perpetrated a mass shooting at a California social services center failed to detonate because it was poorly constructed, two law enforcement officials told The Associated Press.

Investigators believe the couple intended to detonate the improvised explosive device — placed in a bag left at the center that morning by Farook before the shooting — to kill emergency responders or possibly before their attack.

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."

Authorities accounted for the couple's movements using traffic and surveillance cameras, witness accounts and other techniques.

The errors constructing the explosive device and modifying the gun 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.