Complex sentence: By the end of the decade most of the gang members retired, however, Grady would continue operating as a fence later competing against rival fence Marm Mandelbaum who had formed a gang of her own.
Split into simpler sentences: By the end of the decade most of the gang members retired, however, Grady would continue operating as a fence. Later he competed against rival fence Marm Mandelbaum who had formed a gang of her own.