I have a theory. Since this happened only 10 months after the Columbine shooting, could the murderer have had an obsession with the shooting? From the description, the suspect is described as the age 16-20 years old. I am assuming that this is someone they went to school with. The suspect knew who they were. He knew when Nick was working and what time. This wasn’t a robbery, which shows it was not a random person who attempted to rob subway. He knew that he was working alone, closing the store. He may have not know that his girlfriend would be there (there is still a possibility he did know) which could mean he at least could have had the intention of killing Nick or at least students at Columbine High School. The suspect could have had an obsession with the shooting or may have been friends with the shooters. If he knew the shooters, he could have thought he was going to finish their plan and kill the rest of columbine students but stopped after so that he would lay low. In my opinion, this was NOT a coincidence or robbery gone wrong.The suspect knew who Nick was, where he worked, what time he worked, and that he was working alone.