No, I haven't forgotten anything. But I was talking about what could be discovered by biologists, doctors or forensic pathologists. And with the current use of genetic testing, since all life on earth is related (to various greater or lesser degrees) it can be determined through mtDNA, Y Chromosome DNA or Nuclear DNA whether a body was of terrestrial origin or not. Regardless of whether or not it was human.
Putting words in my mouth again? Because that's not what I've said. I'm not sure you even remotely realize what science can tell us. It's a great deal more than you apparently realize.
Actually the opposite is true. Without extraterrestrials (putting humans in space aside) there could be no extraterrestrial craft.