The FBI has a fingerprint and forensic evidence linking Al Qaeda's top bomb maker in Yemen to a trio of explosive devices used in recent attacks on the United States, tangible reminders
that Osama bin Laden's death has not eliminated the threat from the group's most active and dangerous franchise.
Investigators have pulled a fingerprint of Ibrahim al-Asiri off the bomb hidden in the underwear of a Nigerian man accused of trying to blow up a plane over Detroit on Christmas Day 2009, US counter-terrorism officials said. Investigators also determined that the explosives used in that bomb are chemically identical to those hidden inside two printers that were shipped from Yemen in 2010, bound for Chicago and Philadelphia.
The officials spoke on condition of anonymity because the cases remain under investigation.
Bin Laden's death leaves Al Qaeda's core in Pakistan with a leadership vacuum, one that could make the Yemeni branch known as Al Qaeda in the Arabian Peninsula even more prominent.
The Yemeni franchise already had eclipsed Bin Laden's central organisation to become Al Qaeda's leading fundraising, propaganda and operational arm. In a eulogy to Bin Laden posted online earlier this month, the group's leader promised more violence.
"What is coming is greater and worse, and what is awaiting you is more intense and harmful," said Nasser al-Wahishi, who once was Bin Laden's personal secretary.
Al Qaeda's Yemen branch has become so well-known in the US that some commentators speculated in the days after Bin Laden's death that the radical US-born Yemeni cleric Anwar al-Awlaki would succeed him.