Sabotage
The Bat was on the move and had been for a number of weeks, following clues around Gotham leading down various paths in the underworld. Little did he know the Joker was following him and yet remaining one step ahead at the same time (or so he'd like to think). Both got wind of a very interesting shipment coming in at the end of the month that was rumored to have not only the next hot synthetic drug coming on the market but high caliber military-grade weapons.
The Joker had a feeling Batman would want to interfere in his plans, so he planted clues that would lead him in a different direction. As long as he had two hours to intercept the docking and loading, everything will be his!
There's a low cackle building in the Joker's throat when he gets wind that one of his lackeys managed to successfully lead his 'friend' outside of town. This shipment would his! No longer holding back, he's laughing as he moved into the car taking him to the shipyards.