The Obama administration's assassination of two U.S. citizens in 2011, Anwar al-Awlaki and his 16-year-old Denver-born son Abdulrahman, is a central part of Jeremy Scahill's new book, "Dirty Wars: The World Is a Battlefield." The book is based on years of reporting on U.S. secret operations in Yemen, Somalia and Afghanistan. While the Obama administration has defended the killing of Anwar, it has never publicly explained why Abdulrahman was targeted in a separate drone strike two weeks later. Scahill reveals CIA Director John Brennan, Obama's former senior adviser on counterterrorism and homeland security, suspected that the teenager had been killed "intentionally." "The idea that you can simply have one branch of government unilaterally and in secret declare that an American citizen should be executed or assassinated without having to present any evidence whatsoever, to me, is a - we should view that with great sobriety about the implications for our country," says Scahill, national security correspondent for The Nation magazine. Today the U.S. Senate is preparing to hold its first-ever hearing on the Obama administration's drone and targeted killing program. However, the Obama administration is refusing to send a witness to answer questions about the program's legality. "Dirty Wars" is also the name of a new award-winning documentary by Scahill and Rick Rowley, which will open in theaters in June.