(CNN) -- New York Rangers hockey player Derek Boogaard died accidentally due to a toxic combination of alcohol and oxycodone, a Minnesota medical examiner said Friday.
The Rangers' enforcer was found dead May 13 in his Minneapolis apartment. An autopsy was conducted the next day, according to the Hennepin County medical examiner's office.
On Friday, the Minnesota medical examiner announced the results of that autopsy. The office concluded that the "cause of death is mixed alcohol and oxycodone toxicity," ruling the player's death an "accident."
Boogaard's parents decided donate his brain to Boston University researchers studying the effects of concussion in athletes, the Hennepin County examiner said Sunday.
Dr. Robert Stern, co-director for Boston University's Center for the Study of Traumatic Encephalopathy, confirmed Sunday that Boogard's brain was going to be examined as part of a study. The center has a donation registry for athletes so the effects of trauma on the brain and spinal cord can be studied.
Boogaard, 28, began his NHL career with the Minnesota Wild.
The Saskatoon, Saskatchewan, native joined the Rangers in July and appeared in 22 games during the 2010-11 season.
"Derek was an extremely kind and caring individual," New York Rangers President Glen Sather said on the team's website.
"He was a very thoughtful person, who will be dearly missed by all those who knew him. We extend our deepest sympathies to his family, friends and teammates during this difficult time."
Boogaard supported the Defending the Blue Line Foundation, a nonprofit that ensures the children of military personnel get the opportunity to play hockey.
While with the Rangers, he created "Boogaard's Booguardians," which hosted military families at home games, according to the website.
CNN's Ross Levitt contributed to this report.