Complex sentence: Because of his conviction, the estate passed instead to the cousins who had found the silencer in the gun cupboard after the murders, with the flecks of blood and paint that proved pivotal to the prosecution's case.
Split into simpler sentences: Because of his conviction, the estate passed instead to his cousins. It was the cousins who found the silencer in the gun cupboard after the murders, with the flecks of blood and paint on it that proved pivotal to the prosecution's case.