Complex sentence: The trail leads to Mickey Bankes, Alan's mother's boyfriend, who sold it to one John Slater, a dock worker but Slater admits that he was only a go-between and does not know the true identity of his client.
Split into simpler sentences: The trail leads to Mickey Bankes, Alan's mother's boyfriend, who sold it to John Slater, a dock worker. However, Slater admits that he was only a go-between and does not know the true identity of his client.