Complex sentence: Lowery had formerly served as the police cheif the of the City of Florissant until his retirement in 2000 when Stephen Kruse became the new police cheif until Kruse resigned to accept a new position working in the private sector.
Split into simpler sentences: Lowery had formerly served as the police chief the of the City of Florissant. Kruse then resigned to accept a new position working in the private sector.