Complex sentence: After examining the marks, Holmes finds signs of the presence of another man besides Charles and James, who he believes to be the murderer; the person is a tall, limping, left-handed man who smokes cigars.
Split into simpler sentences: After examining the ground, Holmes finds evidence of the presence of another man besides Charles and James, whom he believes to be the murderer. The stranger is a tall, limping, left-handed man who smokes cigars.