I'm sorry to hear about this.
This story is a bit unsettling because my wife and I have a 6 month old rott pup that was 92 lbs at last weight check. I think the standard is about 10 lbs per month so he will be a giant in his breed. My wife did some research while in puppy class and found that rotts can range from happy-go-lucky/goofy to very protective and any mix in between. We are very careful with him simply because his sheer size could hurt people when he's just playing. On our walk last night a group of small kids took a look at him and said, "that's a BIG dog!" Ironically there is a large dane on the street so they should be used to seeing large dogs. We had him sit down, on a leash, before they could pet him. So far he has shown no signs of agression towards anyone or anything, even other dogs eating his food and was once nipped on the nose by a larger dog and didn't even flinch. I have been around other rotts in the past that were great dogs, but did have a side that demanded respect, it is possible he will develop that as he gets older but we are hopeful. I won't put up with him if I consider him a risk to anyone it's simply not worth it.
Do you know if the dog had been fixed? Male or female? Find out if the owner had raised him from a pup. One of the great rotts that I have been around was a friend to everyone but showed a strong dislike for black people. We know she had been mistreated through the fence a time or two, once someone threw battery acid on her face, and we guessed it was an association thing with the person that was mean to her.
I new a guy with an Akita that was going to court because his dog had bitten a kid and the victims parent were trying to get the dog put down. The dog was not agressive and the owner said it was a case of the kid picking at the dog over a long period of time and he reacted with a nip that nobody would have noticed had he not been a large dog. He took responsibility for allowing the situation to occur, but didn't blame the dog for his actions. If I remember correctly, the kid hugged his neck and choked him in the process.
Glad to find someone that isn't a lawsuit freak! Thanks for being reasonable.