What’s the catch for the one million per day?

None

Sounds too good to be true, but I’ll side with that.

insane murderer

Murderer sounds easier to explain to the judge

for the money: would there be taxes on the money? is the money real? is there an ink bomb in it? is the money in cash?
for the murderer: how capable is the killer? are they disabled? what weapon are they using? could the police get involved? how insane are they? how fast are they? are they durable? do they have any backup weapons?

This one's a hard one....