They basically do a statistical analysis on the DNA results of the suspect vs known DNA samples. So they can say something like "it's 85% human" or "it's 95% gorilla".
It's meaningful in that it can EXCLUDE species. So you can say "it's not human" or "it's not a gorilla", and then do a process of elimination. Once you exhaust all of the plausible matches and none fit, you have a new something....