Complex sentence: He proved to be a problem for Gus as he got involved in crime including firearm possession and the theft of charity money, which led to his departure in April 2005.
Split into simpler sentences: He proved to be a problem for Gus as he got involved in lots of criminal activities including having a gun and stealing charity money. In 2005 he was still in criminal activities and this led to his departure in April 2005.