In the story, "On the Sidewalk Bleeding," why did the cop say "a Royal" at the end of the story?

 Andy is the main character in this short story. His
member ship in the Royals, a street gang, has recently been the central focus of his
young life. He took pride in wearing the purple silk jacket and the message that it sent
to those who saw him wearing it: he was a Royal – tough, proud and invincible. When he
was stabbed in the alley, however, he desperately wanted to escape this gang symbol that
led to the attack. In his desperation, he removes the jacket and struggles with his
dying breath to push it away. Still, when the police officer sees a young man stabbed to
death in the street next to a purple silk Royals jacket, he immediately concludes that
the death is due to gang warfare. He never knew Andy personally, but he knows that
deaths such as this one are typical among those involved with gangs. The story suggests
that the case is then virtually closed and the investigation
over