My thought as well - but, fear that the bomb could yet be set off via remote control, cell phone, other means - they took it away to a safe place and somehow blew it up.
I would have liked to know if finger prints could have been lifted from it. Likely not, however.
Sometimes the construction and materials used in the detonator can provide insight as to who is behind the bombing, as can the explosives used. TATP is a jihadi favorite (AKA: "Mother of Satan"), but it tends to degrade over time, and older stock might not go off at all.