Just two days after an NFL player with a history of head injuries committed a murder-suicide, a new study was released connecting even more former athletes to a degenerative brain disease that often leads to depression and suicide. Researchers at Boston University's Center for the Study of Traumatic Encephalopathy have just published their largest study to date that connects repeated mild head trauma to catastrophic brain damage seen in the autopsies of several deceased athletes.

The study looked at 85 people with a history of mild to severe head injuries—including many former high school, college, and pro football players; boxers, and NHL players like Derek Boogaard (pictured)—and found that 80 percent of them showed some evidence of CTE (chronic traumatic encephalopathy) in their brain tissue. Symptoms of CTE include depression, memory loss, cognitive problems, and dementia, but it is nearly impossible to fully diagnose in someone who is still alive, because the brain must be examined directly to confirm the damage.

At least six former NFL stars have committed suicide in the last two years and almost all had displayed some of the symptoms of CTE before their deaths. The Boston University group confirmed the diagnosis in two of them after examining their brain tissue for this study. One of them was Dave Duerson, a former Chicago Bear, who died last year by shooting himself in the chest so that his brain could be saved and donated to the center.

On Saturday morning, Kansas City Chief Jovan Belcher shot himself in front of his coach and general manager, shortly after killing his girlfriend in a domestic dispute. Friends and teammates have reported that he had suffered from football-related head injuries and was battling depression and an addiction to painkillers.