They are trained to detect up to a dozen different explosive compounds, including PETN, the compound that AbdulMutallab is alleged to have smuggled aboard Northwest flight 253 to Detroit on December 25.

CNN: Are dogs the key to bomb detection at airports?

It immediately indicted Mr. Abdulmutallab on criminal charges of trying to destroy an aircraft, despite reports that he told officials he had ties to al Qaeda and had picked up his PETN explosive in Yemen.

WSJ: Terrorist Attempts Attack on Airplane

Plenty of warning signs also preceded Nigerian Umar Farouq Abdulmutallab's attempt to blow up Northwest flight 253 over Detroit on Christmas Day 2009 with an underwear bomb made with PETN, a plastic explosive that was not detected by airport security.

CNN: Agencies often miss warning signs of attacks