Snape wasted no time. There was no need of subtlety or concealment: on the contrary, Snape would need all the power and focus at his command. He knew his Occlumency was proof against Riddle's Legilimency, but the opposite had never been directly tested before. It was quite likely he could fail.
Snape banished all such doubts. A twist of his wrist dropped his wand out of his sleeve and into his hand. He aimed the point between the man's eyes, poised like a scorpion's tail, and hissed "Legilimens!", plunging deep into the man's mind.
The memories washed over him in a frothing, furious spate. The bitterness and jealousy of the working-class drunkard against the silver-spoon-sucking bastards of the world - a sensation profoundly familiar to Snape. He allowed himself a moment of bitter amusement - Riddle certainly likes to stick to certain types of tools - before he slipped deeper.
The memory of the match played out: a sudden spike of resentment boiling over into fury at being shoved aside one more time, pulling his wand, firing Killing Curses. Then, a confrontation with Charlotte Nott, a Slicing Hex that hit his arm, the lustful intention to take her corpse with him, interrupted only by Harry's arrival, and the hasty disapparation.
It was all convincing, consistent, real.
It was all lies.
Snape had seen the man - only at a distance, only through a thick and surging crowd, but he sincerely doubted he could have missed such a standoff, such an exchange of hexes. The only spellfire he'd seen in the man's immediate vicinity had been the unmistakable green streaks of Killing Curses - too many and too virulent to have been powered by the petty little jealousies and spites he saw here.
Snape insinuated himself deeper, tightening his mental grip around the memory, focusing intensely on the start. The spark to the tinder. That spike of rage.
He recalled everything he knew of Riddle's mental style, his love of using the mental weaknesses of others against them, his ability to take the truth and twist it, just enough to suit his purposes.
And he focused. Every tiny detail, every instant. Someone jostled the man... There! The tiniest crack, a fracture in realities. His mind remembered resentment boiling over in fury, but his body... His shoulder muscles tensed, as if the man had been jerked backwards. But in his memory there was no-one behind him.
Fierce triumph filled Snape as he flung everything he was at that tiny inconsistency, that minuscule crack in the armor of memory. He dove on it like a falcon stooping on prey.
And the crack tore wide open. Buried memories hemorrhaged into the gap. Hands on his shoulders, yanking him off balance, into an alcove, trapped with a thing in the shape of a man. Inhuman red eyes, and a hateful voice hissing Invisiperio, tearing his will from him and filling the wound where it had been with a lavaflow of homicidal fury, boiling inside him, impossible to contain, so he spewed it forth in gouts of killing green. Bodies fell before him but it was all nightmare distant, buried behind the agony of knowing that his wand, his will, his mind was not his own.
Snape broke the contact, and heard the other man sobbing, heard himself panting as if he'd just run a race. "Get me a pensieve!" he gasped to Theo, "You'll want to see this for yourself."