The Islamic militant group ISIS beheaded Steven Joel Sotloff, an American freelance journalist who was abducted a year ago in Syria, in a video made public Tuesday by a jihadist monitoring organization. The monitoring organization, SITE Intel Group, announced on Twitter that Sotloff had been beheaded. It said that ISIS had also threatened to execute a British captive, David Cawthorne Haines. Last week, Sotloff’s mother, Shirley, pleaded directly with the leader of ISIS to spare her son. “We have not seen Steven for over a year, and we miss him very much,” she said in a video message to the ISIS leader, Abu Bakr al-Baghdadi. “We want to see him home safe and sound and to hug him.” Sotloff, 31, wrote about conflict in the Middle East for Time magazine and other publications. He grew up in Miami and attended the University of Central Florida in the early 2000s. He has a Twitter account, and last posted Aug. 3, 2013, just before he disappeared. ISIS threatened Sotloff’s life in another video last month. In that video, ISIS beheaded another American journalist, James Foley, and said that it would kill Sotloff, too, unless the United States ended airstrikes against the militant group. The White House press secretary, Josh Earnest, said that he could not confirm the authenticity of the Sotloff video. He said that the United States had devoted significant time and resources to rescuing Sotloff. The CIA also said that it could not confirm authenticity.