dear admiral fans, invest in Kurouma stocks
What if I told you... that Kurouma was Captain Kuro of the 1,000 plans, infiltrating the government under Crocodile's orders?
Post Syrup Village, the Black Cat pirates ran into Baroque Works. However, Kuro massacred them, until some officer stated he should join the organization. But, just as Kuro did join, Baroque Works fell in Alabasta. However, after Marineford, Kuro hunted Crocodile down, and proposed a plan to infilitrate the Marines and destroy them from within.
Now, Kuro is feeding information about the Marines to Crocodile, allowing Cross Guild to pick their targets as they see fit.
Kuro realized he could never truly escape the Marines, and what he really wanted was a life where the Navy was destroyed, so they could never chase him again. So, now, he'll work from the inside to kill as many of them as he can, all while keeping his death secret. Keep in mind, the Navy never found out Kuro is alive.