This weekend’s case of murder and suicide raises familiar questions about brain damage and professional football. Jovan Belcher was an all-star linebacker for the Kansas City Chiefs, described by teammates, coaches, family and friends as “generous and caring.” This weekend he murdered his girlfriend, mother of his 3-month-old daughter, and then shot himself while talking with coaches at the team stadium. The incident is raising again some troubling questions. Almost 4,000 former players are suing the NFL over what the claim is a link between football and long-term brain damage. At Boston University, researchers are investigating possible connections.