I've just caught up with this post, it makes sad reading. WD is there anything on the video that might give ideas? How many birds were killed, was it a single shot weapon, Springer or PCP, anything at all?
Might be worth speaking to local RSPB if they have a local rep/office. Events like this involving working birds of prey are thankfully rare, it may just be that asking around amongst folk like Wildlife reascue etc: may turn up something/someone on the "grapevine." I hate to think of this moron not being hunted..