As drones have become more advanced, the American public has become more aware of the devices. The unmanned flying machines could soon be used by private companies (to deliver pizza, for example) and are already heavily used by the military and some U.S. police forces. With the proliferation of this new technology has come a new public scrutiny.

Today, U.S. Attorney General Eric Holder confirmed that at least four U.S. citizens have been killed in military drone strikes since 2009. According to an Associated Press report, the admission was made in a letter Holder sent to Patrick Leahy, the chairman of the senate judiciary committee.

The strikes occurred in Pakistan and Yemen. One of the drone strikes was targeted to kill Anwar al-Awlaki, an American and Yemeni imam who is alleged to have been a recruiter for al-Qaeda. The three other U.S. citizens killed in drone strikes were not specifically targeted. Al-Awlaki’s son, Abdulrahman, was also killed in the attack, which occurred in Yemen in 2011. An American named Samir Khan was also killed in the drone strike that killed al-Awlaki. Another American named Jude kenan Mohammed was reportedly killed in a drone strike in Pakistan.