Is AUTHOR wrong in the post ? POST : AITA for wanting to get to the bottom of what has happened.

My 10 year old sister recently got two rabbits about 2 months ago and has been obsessed with them. About a week ago I was home alone (I’m a 16 year old male) when my neighbour knocked on the door and asked me to come with her in an almost annoyed  tone. Her dog which poops in our yard regularly had killed one of her rabbits. She said that her dog had brought it to her and that she would buy a new one but she didn’t apologise or even seem upset or at least sorry about it. 

It’s worth noting that this woman and her husband are very weird people . When my family first moved into our house the first interaction my dad had with them was was watching their dog take a dump in the middle of the street  where we live, asking the woman  if she was going to pick it up, and her responding by saying it wasn’t her dog after they both had just seen it happen.

So just today my family got back from a overnight stay at a family friends house and found out that the other rabbit gone missing. The strange thing about it was that there was no holes or anyway that the rabbit could of got out of its fenced in area and when this rabbit has escaped in the past it has always stayed in our yard.  We also found more dog poop in our yard. 
My theory is that her dog killed this rabbit and she found out but it was to awkward for her to tell us so she basically hid the rabbits body from us. 

So at about midnight tonight It was driving me insane (my little sister was crushed) so I went over to her house and jumped the fence into her backyard to go check her bins for the rabbit (when her dog killed the first rabbit she said she would chuck it away until I told her not to because I knew my sister would want to bury it next to our old dog). I successfully got into their backyard and was about to hop down from a high ledge I was on when their dog woke up and started growling and barking at me. I jumped back over the fence before it attacked me. 

So am I the asshole for trespassing or is it justified since all the evidence suggests that it was the same people.