ive read in "five families" that vito Genovese tried to whack Costello because he was hearing about Costello and Anastasia meeting to discuss whacking him.

anyway costello was in vitos way, and vito wanted him gone.

valachi in the "valachi papers" said when vito was in Italy costello was running the family, and valachi said everthing was peaceful when Costello was boss, vito wanted all the power, so Costello was no.1 target,