Complex sentence: Recently some of the former members re-organised themselves as the so-called Nuova Mafia del Brenta and were responsible for a foiled attempt at killing the former founding boss Maniero.
Split into simpler sentences: Recently some of the former members have tried to start with a new organisation, the so-called Nuova Mafia del Brenta. They were responsible also for a foiled attempt at killing the former founding boss Maniero.