Cat killed by wild animal?

How often do cats get killed and disemboweled by wild animals? We need help trying to decide if our cat was killed by some wild animal or worse; by an insane human. Then we need help in trying to decide what to do.

Cat was large 8 month old male, NEUTERED, house cat. He would ask to go out about 3 times a day and would come back in after about an hour. He never went farther than the next door neighbor's homes on either side of us. They all knew him and liked him.

He went MISSING ABOUT 3 WEEKS AGO. We put up posters all over, ran ads in the newspapers, went to all the neighbors, not just the ones next to us, and looked in ALL areas that were woodsy... as we live in town. No cat. Looked all over our yard, under bushes everywhere. No cat. Three weeks, no cat.

Then this morning, on the cement patio right outside our back door... where we go out on several times a day... there he was. Gutted. BUT there was NO BLOOD ANYWHERE AROUND HIM. He was not decomposed. There were no other signs that he had been bitten, broken, anything... just his abdominal contents removed.

Can't understand how he would have come home, AFTER THREE WEEKS, and been killed by a wild animal on our steps. BUT the alternative is that some sick person had him and killed him, and put him on our patio right where we would find him for some sick reason scares us.

There was a nut that came up to my daughter about 4 weeks ago and hit her repeatedly in the face, until she called the police. Then there was cyber bulling that was hateful after that, and before the cat/kitten went missing. I'm just hoping that this happens to cats more than I am aware of, for reasons that don't involve sick humans.

What should we do? Call the ASPCA? Call the police? How can we tell what happened to him?