Complex sentence: He did not believe that Lamb had been mentally ill at any time; he merely had a psychopathic disorder, was capable of all kinds of emotion and was perfectly able to understand the nature of what had he had done.
Split into simpler sentences: He did not believe that Lamb had been mentally ill at any time; he merely had a psychopathic disorder. Lamb, he said, was capable of all kinds of emotion and was perfectly able to understand the nature of what had he had done.