(NewsNation) — The manhunt to find Ayman al-Zawahiri stretched back more than 21 years and ended this weekend after a drone strike killed the top Al-Qaeda leader at a safe house in Kabul, Afghanistan.

Al-Zawahiri was on the FBI’s Most Wanted Terrorist list for his alleged role in the 1998 bombings of the United States embassies in Dar es Salaam, Tanzania, and Nairobi, Kenya. He succeeded Osama bin Laden as the head of the terrorist group Al-Qaeda following his death at the hands of U.S. forces in 2011.

Al-Zawahiri had been in hiding for years and the operation to locate and kill him was the result of “careful patient and persistent” work, a senior administration official told reporters.

The CIA had been tracking al-Zawahiri’s location for months leading up to his death, catching wind of his location after they learned his family had moved into the compound in downtown Kabul he was killed in.

Al-Zawahiri was the “real motivator and planner” for the 9/11 terrorist attacks and the bombings of embassies in Tanzania and Kenya, said former assistant secretary of defense Lawrence Korb.

The reconnaissance operation was in the works for months but escalated at the start of this year after officials gathered critical information about the safehouse at which al-Zawahiri was staying in Kabul.

Intelligence began to go up the chain of command in April and President Joe Biden was briefed periodically during May and June, officials said. Information detailing al-Zawahiri’s routine and living conditions were shared as well as detailed plans of the building he was staying in.

A formal, detailed briefing was given July 1, and the president and the vice president were “deeply engaged” and asked questions about minimizing risks to civilians, according to officials. Biden gave final approval for the strike last Thursday.

The United States does not have any formal diplomatic relations with Afghanistan. The drone strike and the potential repercussions is complicated by the Doha Agreement, which Secretary of State Antony Blinken says Afghanistan violated, NewsNation’s Tom Dempsey explained.

“It was an exchange between the U.S. and Afghanistan where the U.S. would withdraw its forces, as long as Afghanistan would not give be a safe harbor for Al-Qaeda in the country. So Secretary of State Antony Blinken said that the Taliban violated that agreement because intelligence leaders showed that the Taliban knew that I was worried he was staying in the country of Afghanistan, and the U.S. gave no warning of this attack to the Taliban,” Dempsey said on “Morning in America.” “So again, relations were strained even before all this but this strike barely, probably going to make things even more strained between the two countries mentioned.”

“In the face of the Taliban’s unwillingness or inability to abide by their commitments, we will continue to support the Afghan people with robust humanitarian assistance and to advocate for the protection of their human rights, especially of women and girls,” Blinken said in a statement.

The Associated Press contributed to this report.