They are primarily trying to discredit Hersh:

The first of these is by far the shakiest. In early February, Seymour Hersh, the veteran American investigative journalist who exposed the My Lai massacre and the horrors of Abu Ghraib, published a long essay based on interviews with a single anonymous source. The bombs, Hersh claimed, had been planted by CIA divers with assistance from Norway. On closer inspection, however, much of the story disintegrated as Alexander and other researchers exposed numerous inaccuracies.