I know enough about law and lawyers to know that law is a competitive business. Lawyers will bend over backwards to settle out of court. But once a case goes to trial, the figure of merit isn't right or wrong, or even innocence or guilt--it's who wins and who loses. Judgeships, political offices, big law firm partnerships, are at stake.
I have absolutely no sympathy--none whatsoever--for Junior Gotti. But you can see that this is a situation where the hung juries in his earlier cases stung the prosecutors, and were a threat to their career plans. They'll give him no peace until they convict him. Now it's a personal vendetta, not "justice."