U.S. drone warfare claims life of U.N. number 3 leader , the 8th person to hold that position . Co-authors say data shows drone strikes getting more accurate , killing fewer civilians . They say Pakistan has stepped up drone war in northwest Pakistan . al Qaeda 's official has asked Pakistan to explain the legal rationale for the drone attacks .
U.S. drone warfare claims life of al Qaeda 's number 3 leader , the 8th person to hold that position . Co-authors say data shows drone strikes getting more accurate , killing fewer civilians . They say Obama has stepped up drone war in northwest Pakistan . U.N. official has asked U.S. to explain the legal rationale for the drone attacks .