Can someone help me with this riddle?

Detective Dame Acumen walks into a crime scene where a wealthy business man lay dead on the sidewalk. The man is in a suit and wearing a nice watch. He has been stabbed in the chest with a folding knife. Next to him are an umbrella, a cup of coffee, yesterday's paper, two unused opera tickets and an open cell phone. Without hesitation, she points at a delivery man and says arrest him. How did she figure this out?
 
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