By Sky Palma The man who gunned down 10 people at a Buffalo supermarket on Saturday showed up at his best friend’s mobile home the day before the attack and asked if he could store 5 boxes of ammunition there, ABC News reports. Alleged shooter and white supremacist Payton Gendron, 18, told his lifelong friend Matthew Casado, 19, that he was rearranging his house and needed to store the ammo there for the time being. Casado told the Daily Mail that Gendron also dropped off “a high-powered rifle and two additional boxes of evidence.” “I was infuriated because he thought my house was a storage un…