Hi PBB, hope you are well matey.
... This is a topic that I remember well from about ten years ago on the old Alien Hub site. It was started by my good friend Altria and ran for quite a while. I remember that the notion of there being actual examples of truly nefarious aliens that deem it ok to treat human beings in such a disgustingly wicked manner had quite a significantly fearful effect on my psyche for some time.
... It all started with a couple of links such as the one that you posted and specially a couple of lectures about the subject ... chiefly the lectures by a 27 year veteran homicide detective named Butch Witkowski who became a MUFON volunteer investigator.
... as I said, deeply disturbing stuff. And as the thread bloomed we were all digging as hard as we could through known-ufological-history to either confirm or debunk this fearful proposition, and slowly as more work was being done on the research we were finding that though there was enough references to alleged incidents to be found, eg the air force base security guard, the Korean war pilots skinned in their plane, John Lear's myth-starting lie about the human body parts being found in the crashed Roswell saucer etc ... there wasn't any even loosely solid trails, let alone anything that you could describe as being tangible! ... in other words, all leads came to a pretty disappointing end, and in fact there ended up being only the princely sum of three [I think] cases that remained anomalous at all.
And then I did a pretty silly thing to satisfy a little nagging theory that i'd had about the brain scarring [the notion that every excruciating pain inflicted on a conscious human will cause a tell-tale bruise on the brain of the victim] and that could this simply be the work of some other "Human Being" ... could a fellow human being be sick and sadistic enough to inflict such atrocities on his fellow human being? ... And of course I already knew that the answer is a resounding yes! [serial killers, the holocaust etc] ... but like an idiot I had to see 'man's depravity' for myself, ... and went online and found a couple of sites that actually featured Mexican drug gangs actually decapitating people , and also performing unspeakable evil mutilations on fully conscious victims! ... To be honest, It was both strangely engrossing and thoroughly sick... and wish that I hadn't found it, ... furthermore I have to tell you that even to this day those horrible images sometimes pop into my head and I still feel as sickened by them as I did ten years ago! ... so please for heaven's sake do not go there!!
... The upshot of this rambling being that ... no I do not believe that there is anything at all to this 'Alien-Human-Mutilation Claim'. .. other than unfounded sensationalism. .... Unless you can find something solid that I missed of course. ... but tbh, I hope that you don't!
Cheers Buddy.