I disagree

What training did you even attempt with the GSD? 1 year is when they become more self assure and confident and when their personality develops, a lot of dogs change negatively during this period and its usually the same factors. Owners are to soft, dong gets too much affections, has never seen a correction, weak obedience.

A lot of them become more aggressive especially if he has ever had any bad incidences with any dogs while at the dog park or if they see their human as incapable of protecting them.

Did this dog ever see a E-collar? Where they just Pure Positive Trainers? What kind of structure did he have?

I don't know all the things you attempted but putting a dog down at 1 year; I bet I could have fixed the dog or at least you should have found someone willing to try.

I mean if the Dog had tumors was that through an MRI or biopsy done post-mortem. No MRI what if the Dog had a cracked rib which made him on edge you'd and if you did a MRI you could have operated on the Tumors

Cost didn't matter to us.

Yet no MRI done to see if he had any form of broken bones that could be causing this. Like I'm kind of shocked your Vet wouldn't do a MRI to see if there is something psychically wrong with him.

I've seen what you described before; Dog breaks a bone wont show weakness as they are genetically hard coded to not show weakness but the pain puts them on edge every time they see anyone they feel pain which shapes and conditions them. You see a person 10 times and every time you have a pain in your rib you're gonna create that association and start being aggressive eventually.

Pain could have been from the tumor but making that assertion is just an answer of convenience.

My guess is you went to some shitty Dog Trainers who don't know how to fix an aggressive Dog or didnt take enough effort medically to fix any health issues.

My guess is you guys didn't really give the Dog much structure or a single correction. Provided endless attention and Affection and probably were one factor to his issues + the dog had a harder temperament.