Thanks to everyone for your kind words. He was mainly an indoor dog, we would let him out to potty and stretch his legs and one of us would usually be out with him. He spent probably 90% of his time indoors. I usually let him out by himself in the mornings for about 20 minutes while I got dressed for work (around 5am in the morning). Of course it's dark then so he wouldn't go far - his eyesight at night wasn't the best. That morning he decided to go under the house and refuse to come out which is something he's done a few times and he'd always be in the yard when I got home from work so I left him out. I didn't want to leave him out considering the problems we'd been having, but I couldn't coax him out from under there so I had to leave him outside. I guess that's why I feel so terrible about it. If I had of been able to convince him to come out from there so I could put him inside he would be alive today.
The officer said that there really wasn't anything that could be done because there was no witness and no proof to show that they did it. She said she would go out and question them and look around their property to see if she could find anything.
In the meantime, there is more than one way to skin a cat. My landlord said they don't have a septic tank or anything and have raw sewerage on their property so I called the Health Department and they told me to come in and fill out a complaint form for someone to go inspect it. I called CPS to report that they have raw sewerage in the backyard that the kids are exposed to. One of my friends husbands gave me a name and number to call for Code Enforcement to pay them a visit. If I can't nail them for killing my dog then I will nail them another way.
Sneaky, but just. I like it. Keep us updated! and also, make sure they don't find out it was you that called.