A secret government memo was released Monday that reveals that the Obama administration used the war against al-Qaida to justify the use of drones to kill Americans suspected of terrorism overseas. 

The 2nd U.S. Circuit Court of Appeals in Manhattan released the memo after The New York Times and the American Civil Liberties Union filed a Freedom of Information Act lawsuit to have the Justice Department release memos that detailed the targeted killings. The memo says the war against al-Qaida justifies the killings and that a surprise attack against an American overseas does not violate the laws of war. 

The Associated Press reports that the memo justified the September 2011 killing of U.S.-born al-Qaida leader Anwar Al-Awlaki and U.S. citizen Samir Khan. A U.S. drone strike a month later killed Awlaki's teenage son, Abdulrahman al-Awlaki, also a U.S. citizen.

U.S. officials considered Awlaki an "inspirational leader" for al-Qaida and linked him to several attacks on the United States, including an attempt to bomb a plane on its way to Detroit on Christmas Day, 2009, which a Dutch filmmaker thwarted. 

The memorandum states that the killings were justified according to a law passed after the Sept. 11, 2001, attacks that allows the president to use force against people or organizations that planned, authorized or helped carry out the attacks. The memo also says the justification applies to a U.S. citizen who joins a terrorist organization. 

Awlaki had been involved in a thwarted terror plot against the United States and had been plotting other attacks from Yemen. 

According to the memo, Congress authorized the use of "necessary and appropriate" force against the individuals, and the killings were justified because they were in accordance with the laws of war. 

The appeals court ruled that the memo should be released after President Obama publicly commented on the killings. 

ACLU lawyer Jameel Jaffer, who argued the case before the court, told the AP that the memo needs to be disclosed because "the public still knows scandalously little about who the government is killing and why."

"There are few questions more important than the question of when the government has the authority to kill its own citizens," he added. 

Times counsel and Vice President David E. McGraw said the memo is "a critical addition to the public debate over targeted killings and should fuel a richer discussion of the legal and security issues that are at the heart of that debate."

David Barron wrote the memo. He is former chief of the Justice Department's Office of Legal Counsel and currently a judge on Boston's 1st Circuit Court of Appeals. 

Pardiss Kebriaei, of the Center for Constitutional Rights, said the memo's contents show the program was built on "gross distortions of law."

Kebriaei, who worked with the ACLU on two lawsuits challenging Awlaki's killing, estimates that U.S. drone strikes since 2009 may have killed more than 4,000 people. 

"The United States' loosening and redefining international rules governing the use of force and war is ultimately not going to make anyone any safer," Kebriaei said. 

The 2nd Circuit Court has also ordered the Justice Department to disclose other legal opinions to decide if they too should be released.