A Wisconsin baby sitter is accused of killing a 2-month-old boy and pretending he was alive when she gave the baby back to his mother. Marissa Tietsort, 28, is charged with first-degree intentional homicide. Police said Tietsort killed the infant with blunt force trauma, then put him in a snowsuit and car seat and returned him to his mother — without telling her the child was dead. Authorities found the mother trying to revive the boy. Tietsort told police she didn't kill the baby, but knew he was dead. She said when her boyfriend got home they went to McDonald's and she brought the dead baby with them. After she gave the boy back to his mother, Tietsort, her boyfriend and their son went swimming at a local hotel, the complaint said.