So to further add to my guess. Ein is a person maybe police maybe CIA FBI whatever. He wen...

Ein was working in Germany at a restaurant. He was in contact with a man called Yarek who was involved in some crimes related to money a drugs. When Yarek was going to collect what he was owed from the priest, he discovered Diesel restrained, drugged and injured, and he took him to Ein. Yarek was able to arrange for a private doctor, so that was the last time they saw each other for a few months. When they met again, Ein thought that Diesel appeared not human, and followed Diesel and Yarek to a pub. Ein tried to get more information about Diesel's background, thinking he may be an immigrant and a victim of human trafficking but didn't succeed. Diesel told him, in German that Yarek calls him Diesel. So Diesel's real name, nationality, where his dad is etc have not been divulged. Yarek was in the pub grumbling about the priest, and a rival gang tried to attack him. Diesel sprung into action to defend Yarek and cut off the man's finger. Diesel tells Ein, when asked that he sensed what was going happen due to the scents. Later Ein discovers Yarek and Diesel having sex. Yarek is likely the man who Ein killed, fot reasons unknown. Ein and Diesel have been in SK for a couple of years, and the Chief wants Ein to return to Germany. When the official translations come out, it might be clear how they were linked to the wider European gangs. And that's been about it, but Diesel doesn't have a pack, it was just him and his dad, and now he's in Germany, alone with no identity.