Complex sentence: Often, he would stand when he said it, adding a subtle threat; he always wore a suit, and his jacket would be open when he stood, giving him the mien of a plain-clothes cop.
Split into simpler sentences: Often, he would stand when he said it, adding a subtle threat to the situation. He always wore a suit, and his jacket would be open when he stood, giving him the mien of a plain-clothes cop.