My 17mth GreatDanes unexplained death

Question:
 ???Last Friday I came home from work and found my beautiful 170lb Great Dane Bremen laying in the drive way dead. He had blood coming from his mouth. He had some scrapes on his back but no blood at all on his body. Just the dark blood under his head and still in his mouth. I ran to him and put my hand on him and he was still warm but stiff. He had just died. The neighbor across the street had seen him earlier and he was fine. She never heard him bark and never saw any one close to the house... He was so big and so friendly but if anyone had come into the yard he would jump up and down and bark. At first I thought someone had shot him...of course the neighbors would have heard that...we called the police and they had no idea what happend. There were no wounds on his head or his body. Other than the marks on his back and leg. But no blood . I think maybe it was bloat...but they don't vomit when they get that do they...and why would he have blood in his mouth. Ive read about bloat but they dont mention that there is any bleeding..His stomache was flat not distended or anything unusual...This has been so hard for us..He was our buddy he still thought he was a puppy and wanted to lay in our laps. He loved us and we loved him...I feel so horrible that I wasn't there when he needed me. At first the possiblities were to painful to think about. Now I need to know what happend to him. I hope someone can help. Thank you
Answer:
 Thank you so much for your reply. He was chained in front of the garage. He normaly was in the back yard but it was muddy and we put him there where he could be outside and not get mud all over him. He was far off the road. I never thought of him falling but we have a retaining wall that he would climb on sometimes. I think with the vomit near him it had something to do with his stomache...I don't know any thing about the tell tell signs of poisoning either...I was so distraught when he died the police came but when we took him into the 24hr vet place to take care of his body...I really just was so upset I couldn't even think about the autopsy or anyone doing anything to him...we wanted to bury him but it would be like buring a horse in the yard and I didn't want anything to dig him up that would be a night mare....thank you for reading my post and for your reply...Im so sorry about your loss. I feel like there is a huge void in my home now...and I can't stand to be here. I hope in a few days or weeks you can find the joy in your memories and enjoy life again. I believe God puts animals on this earth for us to enjoy and to love and take care of but to teach us something about ourselves. Bremen taught us so much and we are changed for the better because of him. I guess his job here is done. Some books don't have many pages but there still great books....
Answer:
 are you sure he wasn't hit by a car?if he was it could have been mostly internal damage.was there a high place he could have fallen from this can also cause a lot of internal and not much external damage.i think bloat does cause vomiting,i've never heard of it causeing bleeding either,i think the belly is always distended but i don't know if it goes down after they pass.did you ask for an autopsy in case it was poison some poison will make you vomit blood but that wouldn't explain the scrapes unless he got under something and scraped himself up.do you have a porch or crawl space that might have poison under it?i'm sorry for your loss,i know how hard it is my boy kyena was 16 and he's been gone for the longest month and a half i've ever expierienced.