The Joker hasn’t been seen for a while and it was concerning.
Danny just wanted to live a quiet life, well as quiet as an un-aging and immortal could live in a new dimension. He swears it was an accident. He didn’t mean to kill the weirdo clown. In his defense, the clown attacked him first. In his panic, he forgot about reporting the incident to the police and figured hiding the body was the best bet.
He just didn’t expect to be caught.
The last thing Jason expected when walking around Gotham was to catch a teen hauling Joker’s dead body through the park and attempting to bury it.
So he did what any Gothamite would have done when confronted with Joker’s dead body.
He offered his help.
Imagine their surprise when they realize they were neighbors.
Well as they say, people who bury bodies together, stay together.