How can I be certain my neighbor's dog died from ingestion of lighter fluid?

My house is about 200 feet away from my neighbors, though we share about 2 acres of yard all around. They had an outdoor dog who was just under a year old. The other night, my dog had to go out to do his business at about 4 in the morning, and I saw that the neighbor's dog was fine, because she ran up to play. The neighbor also saw she was OK at 5am when she got up for the day, and she seemed OK. Then, at 9 in the morning, the neighbor found her dead at her doorstep. She had blood coming out of her mouth and rectum. At first, we thought she was poisoned, because she roams the road a lot and another neighbor has chickens she may have gotten into. Another possibility was she was struck by a car and made it to the doorstep. Now, about a week later, we noticed that our lighter fluid that was on our grill on the front porch was missing , and found it near the woods and that it had been chewed and was missing over half. My question is, what are the signs that a dog would have ingested