Just for fun I came up with an alternate scenario that also meets all of the facts as we know them-
Gatti: Knocks on door of Homeowner (named Mr. Smith) at 8pm
Smith: Looks out peep-hole, sees and recognizes, Gatti, opens door
Gatti: "Smith, I'm tired of you blowing me off, I really need that $5,000 I loaned you"
Smith: Turns his back and walks into his living room
Gatti: Follows him in
Gatti: "Smith, I'm serious, when you came to me begging for money because of your stupid bets on the Kentucky Derby, I took out a damn credit card advance to help you out"
Smith: "How the hell was I supposed to know a 50 to 1 shot was going to take them damn thing??"
Gatti: "I don't care about the damn bet! I helped you out and I need the money back!"
Smith: "Okay, I have a partial payment, follow me into the bedroom"
Gatti: "Great, thanks Smith!"
Gatti: Follows Smith into back room
Smith: Reaches into top drawer, grabs revolver, turns to face Gatti
Gatti: "What the EFF Smith!? Fine, don't pay me! Just don't shoot!!"
Smith: "Eat lead you stupid mother-effer!!!" BLAM-BLAM
The End.