[ WP ] You 're a University Professor , and a retired Detective . You 're using a cold case that you were the lead detective on as an example in class . Afterwards , a student confides in you . He knows who did it .

`` What? But that's not possible,'' I stammered. `` Not even the best detectives I've had the pleasure of knowing could figure it out.'' Surely the boy was reaching, making connections where there were none. 
 
 `` I assure you, sir, I know, with certainty, beyond the merest shadow of a doubt, who did it.'' His eyes gleamed with the thrill of outsmarting his teacher, one-upping the old man. 
 
 `` And I assure *you*, that's simply not possible.'' He laughed in my face. Cocky, headstrong. Much like a younger me. 
 
 `` The clues were there, plain, obvious,'' he said through stifled laughter. `` Your colleagues must have been blind.'' 
 
 `` Walk me through your process, then,'' I asked, `` if you'd be so kind.'' 
 
 He rattled off a list of seemingly-unrelated things, which, viewed from this side of the years since the case went cold, formed a clear pattern. A shoe-print here, a thread there. `` And the most damning detail, the piece that told me, once and for all, who it was?'' 
 
 `` Do tell,'' I said, drawn in by the brilliant work this young man had done. 
 
 `` You're still wearing the same shoes you did that day. Scuffs and all.'' 
 
 I stood, shocked. This boy had done what no one in the entire police force had been able to do to this day. 
 
 `` Do n't worry,'' he smiled. `` I wo n't tell if you wo n't.'' I only noticed then the knife just barely protruding from his backpack, the gloves hanging from his pocket.
