The Muslim who was arrested on Christmas day was attempting to detonate a bomb; the bomb consisted of a device containing Pentaerythritol Tetranitrate (PETN), Triacetone Triperoxide (TATP) and other ingredients. And, the Haskell's are helpful enough to publish a blog describing their experience with the terrorists (plural) during the incident. The FBI report of the incident has changed numerous times, but has not confirmed the detention of a second individual. According to the Haskell's the bomber had an accomplice and they maintained this point consistently.
Another passenger, Daniel Huisinga, supports the basic claims by the Haskell's.
A third passenger on the flight, interviewed with the Haskell's on CNN, confirms the details of their account; in addition, a man with a camcorder apparently taped the entire incident.