How many games of doubles Zoo Keeper did John Lexmark play? Provide an explanation
Zero. Lexmark doesn't play in public.
Partial credit. The answer is correct and was the most obvious part of the puzzle. The bigger mystery is really about the murder and its singularity.
The sordid tale of the party itself is a bit more complex than at first glance.
Lexmark shows up at Marcus' party with his friend Flossy not knowing what is in store that night.
Lexmark is surprised at the other guests that have shown up, then when he sees Marcus has acquired a Zoo Keeper he starts to sweat. When Marcus starts with his mixer game to get the party going, Lexmark panics, knowing he'll have to finally show his play in public. He starts to calm down a bit and think things through. Fortunately for him, the only two attendees he's met before are Marcus and Flossy.
As a true competitor, Lexmark could never play a public game of Zoo Keeper in front of Dean and Jason and reveal his precious secrets. Marcus clearly had to go.
But what about Flossy you ask? Flossy wasn't murdered? Lexmark had to play Flossy! Ah, yes, the problem with Flossy. As Lexmark sharpened his knives, he reread the rules of the mixer game and noticed a glitch he could exploit! The rules only required people to play games, and Flossy was a sheep!
As the police showed up, Lexmark thought he'd get away with it too, by blaming it on those "troublemakers" in the CAG community that had been persecuting him. Unfortunately for him those meddling kids over at the Donkey Kong Forums sorted the mystery out and brought him to justice.
Disclaimer: All characters appearing in this work are fictitious. Any resemblance to real persons, living or dead, is purely coincidental.