Slade decides he's gonna do Dick a favor. He's gonna end this stupid war for Gotham or whatever deranged nonsense the Bat is up to now, and add it to the list of 'favors' Dick owes him. And he knows how to do it.

He's gonna act like the Bat himself put a hit out on the smartest bird, the first Robin's first acknowledged brother; he's going to pretend to gun for the bo-wielding Robin at the Batman's request.

He knows the man's slipping mentally, it's fairly obvious.

So he gets his resources together, lays a false trail, and starts "hunting" the third Robin. He leaves hints, clues, things like that. Brags to Nightwing that if Robin III is expendable to the Batman, then how long until he tries to take Nightwing out as well. He gets very, very close to taking out the little Robin once or twice; one time the newest, youngest Robin stopping him with a positively feral look.

It is, in a word...fun. High stakes tag, so to speak.

It doesn't take long before Batman is convinced he put a hit out on one of his own birds.