He has dispatched his own brother to death, hiding a bomb on him before he crossed into Saudi Arabia to target the kingdom’s chief counterterrorism official. He has tried to attack the United States three times in the past three years, building small, sophisticated and hard-to-detect devices in his workshop in the rugged terrain of southern Yemen.

Ibrahim Hassan al-Asiri, who hails from a middle-class Saudi family, is the top bombmaker for al-Qaeda’s Yemen branch. Only 30 years old, he represents the CIA’s worst fears: a highly skilled terrorist determined to attack the United States.

American officials believe Asiri’s latest bomb was designed to be smuggled onto a U.S.-bound aircraft last month. The non­metallic device had an advanced detonator and was superior to anything created by terrorists so far.

“Asiri is an evil genius,” said Rep. Peter T. King (R-N.Y.), chairman of the House Homeland Security Committee. “He is constantly expanding, he is constantly adjusting.”

U.S. intelligence and law enforcement officials have said Asiri built the bombs in the attempts to bring down a commercial flight near Detroit and two cargo planes headed for the United States. King said the latest bomb, part of a foiled plot, appeared to be “a modification of the previous ones.”

With the death of Osama bin Laden, Asiri is a key reason that U.S. officials consider Yemen’s al-Qaeda in the Arabian Peninsula, or AQAP, to be one of the most significant threats to the American homeland.

“He is highly determined and fully committed to attack America,” said Mustafa Alani, director of security and defense studies at the Gulf Research Center in Jiddah, Saudi Arabia. “For al-Qaeda, an attack inside the U.S. is worth 11 attacks outside. It has become their obsession.”

Over the past year, AQAP has taken advantage of Yemen’s political turmoil and seized large swaths of territory in the south. Yemen’s government and the Obama administration have responded with aerial assaults and drone strikes, targeting Asiri and other top operatives of AQAP.

Asiri built the “underwear” bomb worn by Umar Farouk Abdulmutallab when he tried to blow up a Northwest Airlines flight headed to Detroit on Christmas Day in 2009. A year later, Asiri built the printer­-cartridge bombs that al-Qaeda placed on Fedex and UPS planes destined for Chicago.

If it were not for a technical problem (Abdulmutallab’s device failed to detonate) or solid intelligence tips (Saudi counterterrorism officials alerted authorities in Dubai and Britain to intercept the cargo planes), Asiri would have succeeded in staging a catastrophic disaster in American skies.

“Ibrahim al-Asiri is the one who enabled the operations of al-Qaeda in Yemen to move from local attacks to international ones,” said Said Obaid, the Yemeni author of a book about AQAP.

A chemistry student

Asiri’s family hails from southwest Saudi Arabia, near the Yemeni border, the region that was home to several Sept. 11 hijackers. But nothing in Asiri’s childhood suggested that he and his brother Abdullah would turn to jihad. Born in Riyadh in 1982, Asiri is the son of a Saudi military officer.