On the ice, Derek Boogaard was a bruiser, chalking up more than 60 fights over his six-year National Hockey League career.

Off the ice, he fought a different type of battle. Boogaard had an addiction to painkillers -- one that would ultimately take his life in 2011.

Now, new information obtained by TSN and CTV's W5 show that the Medical Board of California is looking into one of the NHL’s top doctors. David Lewis is currently being investigated for how Boogaard’s case was handled after he was released from a Malibu rehab facility.

The case stems from a complaint made by Derek’s father Len Boogaard, who obtained his son’s medical files.

"I just want to know why. Why they let it happen,” the former Mountie said. “You know there was no need for my son to die. All the checks and balances were in place but they ignored it."

Records show that during the last six months of Derek’s life, he failed 14 out of 19 drug tests. The document shows Boogaard tested positive for drugs like diphenhydramine and pseudoephedrine – found in Benadryl and Sudafed – but also morphine, oxycodone and other painkillers.

(You can a read a record of those failed drug tests at the bottom of this story.)

Despite this, NHL and NHL Players Association doctors didn’t suspend the New York Rangers left winger.

“It's a tragedy and a poor reflection on a system that's supposed to catch them and help them," says sports anti-doping expert Stuart Phillips.

For 20 years, the league has had a program in place to deal with substance abuse. League and union doctors are able to discipline players for positive drug tests.

In Boogaard’s case, that didn’t happen.

"They are in the entertainment business. They are looking at how to drive profit,” says Paul Melia from the Canadian Centre For Ethics in Sport. “Where does the health and safety of their players fit?"

Recent emails from NHL executives show officials wanted less interference from medical professionals when it came to dealing with head injuries.

In an email sent months after Boogaard’s death, NHL deputy commissioner Bill Daly appeared to link head injuries to problems off the ice.

"Fighting raises the incidence of head injuries/concussions, which raises the incidence of depression onset, which raises the incidence of personal tragedies," Daly wrote.

CTV News reached out to Lewis and the NHL repeatedly, but received no response to requests for comment.

With a report by TSN Senior Correspondent Rick Westhead