A Cohasset man accused of killing his brother-in-law at a birthday party in May has been cleared of all criminal charges, Norfolk prosecutors announced Monday. John McDonough, 46, was charged with manslaughter and assault and battery after getting into a physical altercation with his brother-in-law, David Hoelzer. Police said Hoelzer had become unruly after consuming too many alcoholic beverages and McDonough put him in a headlock. Both men fell to the floor, but Hoelzer never got back up. The case was dropped after a grand jury declined to issue an indictment after reviewing the evidence presented to them, including an autopsy report and other information pertinent to McDonough’s arrest.