In 1955, in the alternate timeline where an elderly Biff Tannen traveled from 2015 to 1955 with a Grays Sports Almanac to make himself rich, Biff drove his grandmother to Las Vegas so she could play the slot machines. Biff wasn't allowed to bet at the Turf Club because he was underage, and when he convinced his grandmother to bet for him, she gave him back the money he gave her to place the bet, and kept the profit for herself.
Outside the Turf Club, Biff met a shady man named Uncle Lou. He promised Biff that he would help him win, but he only wanted Biff's secret to picking the correct winning team for himself. Lou killed Gertrude and put her in the back of the car, then took the almanac from Biff. Lou tried to kill Biff, but Biff caught Lou's crowbar and used it to kill him instead. Biff took Lou's briefcase full of money, and drove his car out to the desert. He buried Lou and his grandmother there.
He then drove to Al's Photography and used Lou's money to buy a counterfeit death certificate that stated Gertrude died of natural causes and was cremated. This certificate convinced the Hill Valley Police Department, which came to the Tannen residence thirty-six hours later, and left, telling Biff that they were sorry for his loss.