this is so sad what should I do?

The reason why the cops didn't pursue an investigation is because there is no evidence and it's hard to prove.

You can take out an ad and post local signs and offer a reward for anyone coming forward and giving you a tip that leads to the arrest and conviction of this person. That's about all you can do.

Why can't she have other pets? She simply needs to lock her door and leave keys with caretakers or trusted friends in case there is an emergency.

You don't say where this happened? Is their an ASPCA in the area? Do they have investigators? I would knock on a few doors and see if any of the neighbors saw anyone in the neighborhood around that time period. In the cases of killed animals cops will not pursue anyone without a direction to go in. Your friend needs to go down to the Police Station and push. Someone came in her home- push with that and see what you can find out. Contact the local paper and local TV station and see if you can get them to write a piece on it/do a story. Idiots talk- offer a reward- be proactive- get in touch with cat people online in your area- make it a big deal because it is. If your serious and keep pushing you never know what you can accomplish.

there is only one good reason i can think of as to why the cats were killed. someone left rat poison out and the cats somehow got to it. anyone else would have done this just to be evil.

don't get me wrong, i love cats. but with this type of situation, i think it would be best to help your friend get a new cat and try to forget about the situation. if the cops won't pursue this issue, there's nothing left to do. i hope that all goes well if you take my advice.

Any ideas for what? You haven't actually asked a question here.