Lilo basically summed it up.

Drugs had supposedly been one of several reasons why there had been tension between Bruno and Caponigro for years. Caponigro was brazen and ambitious and reportedly didn't care for Bruno's more laid back approach.

Bruno's stance on drugs was similar to Castellano's. He didn't want his own guys involved but he readily took drug money off other Mafia narcotics traffickers who operated in his territory; the Sicilian "Cherry Hill" Gambinos, for instance. Of course, Caponigro felt they were losing out on a lot of money.

Bruno's flexible stance on Atlantic City, as far as the NY families go, was the last straw for Caponigro, who was behind his death - some say personally.

As Lilo alluded to, Frank Tieri basically gave Caponigro enough rope to hang himself, afterwards taking over the disputed gambling operation in Newark. Guys in Vincent Gigante's crew were reportedly the ones that picked up Caponigro and his driver - never to be seen alive again. Gigante also gave the OK for several additional murders in the Philadelphia family. And through Bobby Manna's ties to Nicky Scarfo, they had an inside track to HERE Local 54 when Scarfo became boss.