If they can get a bone or a tooth it will be enough.
If this guy was in the same place at the same time the girl went missing he probably did the crime. He sounds like a real piece of shit. I would be in favor of tying a thin rope around his testicles and hanging him on a tree until his testicles ripped completely off. After that happened they should fill his wound with alcohol and salt. They can leave him there to die a slow painful death.