One day before President Obama was scheduled to deliver a a major national security speech to discuss his administration's evolving counterterrorism policies, the White House for the first time acknowledged using drone strikes to kill four American citizens living in Pakistan and Yemen.

According to the New York Times, which obtained a letter Attorney General Eric Holder sent to Congress discussing those strikes, the administration has admitted to deliberately killing Anwar al-Awlaki, a radical Muslim cleric who was a member of Al Qaeda's Yemeni affiliate. Holder wrote that the government had not "specifically targeted" the other three individuals, implying they had been killed inadvertently.

While it had been widely reported that a U.S. drone had taken out Awlaki, the government has never before confirmed that to be true. The administration has, however, defended the use of drone strikes against American citizens in the past, and laid out a very rough guideline under which such attacks can be used when there is an "imminent threat of violent attack."

Holder's letter suggests Awlaki fit within that rather capacious framework.

"Moreover, information that remains classified to protect sensitive sources and methods evidences Awlaki's involvement in the planning of numerous other plots against U.S. and Western interests and makes clear he was continuing to plot attacks when he was killed," Holder wrote, according to the Times.

The revelation sheds some new light on the controversial program, which civil rights groups contend is a direct violation of the constitutional guarantee to due process. However, it does not offer any more details about the government's definition for when such strikes are warranted and lawful.

While the president probably won't divulge too much about his administration's most secretive operations on Thursday, it's expected that he'll more fully answer that lingering question about secret drone strikes. It's part of an ongoing effort to create a so-called "legal architecture" that would take the drone program out of its legal gray zone, and impose safeguards that would prevent its abuse in the future.

Here, three other big questions observers hope he'll answer in his speech:

Whom can the government kill with drones?
The administration faces questions not only over its rationale for killing Americans with drones, but more broadly over its legal justification for killing just about anyone suspected of having terror ties. Indeed, it has been reported that the U.S. has taken out non-Al Qaeda Islamic extremists who appear not to have posed any direct threat to the United States.

As Wired's Spencer Ackerman notes, the administration's vague definition of what constitutes a terrorist or a terror threat has left incredible ambiguity about whom the government can target and kill.

"The broader the definition gets, the more the war sprawls — and the more distant victory becomes," he says. "But it is to observe that after 12 years, the government lacks a rigorous understanding of who, exactly, is its enemy. You cannot win a war that way. You can only send the drones to more and more places, killing more and more people."

Who should run the drone program?
A second sticking point has been whether the U.S.'s drone program should be primarily run by the CIA — thus allowing it to remain largely under wraps — or by the Pentagon.

The CIA has long maintained that it can't even acknowledge the existence of a drone program. Back in March, a federal appeals court ruled that the CIA's position was neither "logical nor plausible," since senior administration officials, including Obama himself, have discussed past strikes. Yet that didn't force the CIA to reveal any new information, and the program remains veiled in secrecy.

According to Reuters, the president is preparing to hand over some drone operations to the Pentagon, a move that should make the program more transparent, since the Defense Department comes under Congress' oversight authority. However, Reuters added that it was uncertain if Obama would announce that decision Thursday.

Will the government finally close Guantanamo?
An administration official told the Washington Post that Obama "will review our detention policy and efforts to close the detention facility at Guantanamo Bay" in his speech, though the official did not offer any specifics. With hunger strikes mounting at Guantanamo — of the 166 detainees still being held there, more than half are now refusing to eat — Obama earlier this year pledged to close the prison.

Obama made that same vow four years ago, declaring in just the first few days of his term that he'd shut it down. Yet Congress blocked his initial efforts to try prisoners in civilian courts and transfer detainees to mainland prisons, leaving the Guantanamo's fate in limbo.