Alexanda Kotey and El Shafee Elsheikh are said to have been part of the terrorist cell that beheaded numerous British and American citizens, including the journalist James Foley. The pair, currently detained in Syria by Kurdish forces, are likely to stand trial for these crimes in the United States. Part of the reason Guantánamo Bay remains open is that it can be extremely difficult to secure convictions in such cases; the US will want as much evidence as possible, and the UK, which has been gathering intelligence for years, will have a lot.