Do male hen harriers even visit the nest before the eggs hatch? Having read up on it I suspect not!
He will visit on occasions to drop off food for her whilst she is sitting hard, but normally they exchange food in the air. Sometimes a Male will service and feed two females and you would never trap a male at the nest. No point in setting a trap in the nest, much easier to walk up to it if you want to kill the hen and evil men will know this. She will fly at you initially so very easy to shoot.
The whole thing has to be a set up, just like the eagle" killed "in the Borders a year or two ago. The policeman holding up a dead eagle might have believed it to be true, but it was not that eagle he was holding up, I know because I worked on that beat for two years and "My Eagles" had been there for eight years before that and I could identify that hen out of any twenty eagles. It makes you wonder how many dead birds of prey reside in fridges or freezers belonging to antis to be used as and when required.