Former NFL star Junior Seau killed himself on Wednesday with a self-inflicted gunshot wound to the chest. No suicide note was found, and people are searching for answers.

Why did Seau end his life at just 43 years old?

Seau's death has led many to believe that the former linebacker was suffering from some sort of head trauma from playing in the NFL. His family says he did not complain about pain resulting from concussions, but one former teammate of his says Seau suffered countless head injuries.

Gary Plummer played with Seau in San Diego. He told the San Jose Mercury News that Seau suffered approximately 1,500 concussions in his playing career.

In the 1990s, I did a concussion seminar. They said a Grade 3 concussion meant you were knocked out, and a Grade 1 meant you were seeing stars after a hit, which made me burst out in laughter, said Plummer. As a middle linebacker in the NFL, if you don't have five of these (Grade 1 effects) each game, you were inactive the next game.

Junior played for 20 years. That's five concussions a game, easily. How many in his career then? That's over 1,500 concussions. I know that's startling, but I know it's true. I had over 1,000 in my 15 years. I felt the effects of it. I felt depression going on throughout my divorce. Junior went through it with his divorce.

Seau's family has agreed to allow the former player's brain to be studied to see if he was indeed suffering from any concussions he incurred during his days in the NFL.