Maria shot the player character ("Claude") at the end of the game.She was talking to distract him. He was shaking his head, facing away from her and she killed him. She stopped talking to pull the trigger. The whole game was an Evil Plan by Maria to get rid of all of her enemies.
("Claude") shot Maria at the end of the game.Similar to above, but Claude, after all he went through the game, shoots Maria to put an end to her. He shoots and kills her and moves on with his life with most of the gangs wanting him dead.
Claude shot himself at the end of the gameYet again, similar to the above WMGs, Claude felt guilty about all of the murder he had committed at the end of the game and decided that he'd only let one more be added to his body count.
Claude shot Maria... but not just because she was talking too much...You know the last time we saw Maria? Y'know, before she was "kidnapped" by Catalina? She was torturing Miguel, the Colombian mob boss, with Asuka, the Yakuza mob boss, to get dirt on Catalina's SPANK operation. After this appearance, Maria kills both Miguel and Asuka, and "kidnaps" Maria. Seems like convenient timing? Nope, Maria was The Mole all along, and was helping Catalina to wipe out her remaining criminal competition in Liberty City. Either that, or she took Salvatore Leone's position in Catalina's drug trade after Claude capped him. Either way, the "kidnapping" was all staged to lure Claude into a trap. Maria kept up the ruse after Claude blew Catalina out of the sky to save temporarily save her hide, but Claude, even being ambiguously Dumb Muscle for any mob boss that asked him to do a favor, was smart enough to put two and two together, and made sure Maria was Rewarded as a Traitor Deserves.
The gunshot at the end of the game was a surviving Colombian gang member:Claude spotted a Colombian member who survived the incident and finished him off Maria stopped talking because the gunshot startled her :]]