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 Usama 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, U.S. counterterrorism 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 last year, 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 organization 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 United States that some commentators speculated in the days after bin Laden's death that the radical U.S.-born Yemeni cleric Anwar al-Awlaki would succeed him. But U.S. officials and counterterrorism experts say that's extremely unlikely, given his American citizenship, his relative newcomer status, his 1997 arrest in San Diego on solicitation of prostitution and the fact that he's not even the operational leader in Yemen.

The FBI has been building cases against a number of high-profile terrorists, including al-Asiri and al-Awlaki. For now, though, there is no guarantee those cases will ever make it to a courtroom. President Obama has not indicated what he would do if a major terrorist suspect was captured abroad. It's a politically sensitive issue because, even though civilian courts have been used for years to prosecute terrorism cases, Republicans have portrayed Obama as weak on terrorism whenever he discusses that option.

Intelligence officials long have believed al-Asiri helped build the Christmas and cargo bombs but have never disclosed how they were able to directly link him to the failed attacks. The fingerprint also would help establish al-Asiri's identity if he ever were apprehended, possibly allowing the Justice Department to extradite him to the U.S. for prosecution.

It's not clear who provided the FBI with the original fingerprint used to match the one lifted from the underwear bomb. But it probably came from Saudi Arabia, where al-Asiri and his brother were arrested for their involvement in an Al Qaeda-affiliated terrorist cell. They were released and later fled to Yemen in 2006.

In March, the State Department designated al-Asiri a terrorist and banned Americans from doing business with him. The U.S. said he was also involved in planning to bomb Saudi oil facilities.

He's also implicated in the 2009 attack on Saudi Deputy Interior Minister Prince Mohammed bin Nayef, the country's top anti-terrorism official. Intelligence officials say al-Asiri strapped a bomb on his younger brother, who volunteered for the suicide mission. The attack killed the younger brother but only managed to injure Nayef.

Though the device was dubbed the "butt bomb," explosives experts believe the younger brother had actually held the bomb between his legs.