Last week [April 11], following the failure of the criminal proceedings to shed significant light on underlying causes and culpability behind the Lac-Mégantic disaster, the Québec National Assembly passed a unanimous resolution calling on the federal government to hold a Commission of Inquiry.Transport Minister Mark Garneau responded immediately that an inquiry was out of the question. His reason: there have been several investigations notably the Transportation Safety Board [TSB] report, which he deemed to be the last word on the tragedy.This is simply not true. The TSB report, while important, is no substitute for a Commission of Inquiry. It is limited in scope, cannot assign blame, and unlike a public inquiry, is not able to compel testimony from major players in public, under oath, and subject to cross-examination.There are many unanswered questions about what happened and who was responsible. The citizens of Lac-Mégantic are owed the full story behind the event that so grievously affected their lives.The TSB report listed 18 causes and contributing factors. The vast majority related to the company itself and its employees. Only one cause related to Transport Canada headquarters, where all major regulatory decisions were made: that it was aware of significant operational changes by the company and did not provide the necessary oversight of these changes. This vaguely worded cause obscures more than it elucidates about Transport Canada's role.More troubling: the preliminary [non-published] version of the report listed as a cause Transport Canada's granting permission to the company, MMA, to run its oil trains with a single crewmember. This cause was erased from the final report. Why? Who wanted it removed? What influence did they exert? Was there political interference? Was the TSB's independence compromised?Who within Transport Canada made the decision to allow this delinquent company to operate single person crews, despite major opposition within Transport Canada itself? Is there a deeper organizational dysfunction within the Department and a much too cozy relationship with the railways?All the legal actions were settled behind closed doors without going to trial, except for the criminal case against the three front-line workers. And what qualified as admissible evidence in that trial was so limited as to exclude even the TSB report.The only people who testified were low-level company employees, a government inspector and police investigators. No company executives, no senior government officials; no politicians responsible for overall regulatory policy; no industry leaders—were compelled to testify.Powerful government insiders and industry players have an interest keeping in the whole truth about the role of a deficient regulatory oversight regime and company self-regulation in the disaster, from becoming public.Transportation of diluted bitumen by rail in Canada is on the increase. The International Energy Association estimates traffic will double over the next two years. Given the uncertainty surrounding Kinder Morgan, the increase could be substantially prolonged.The Prime Minister's case for pipelines is based in part that they are safer than rail. The validity of this assertion aside, massive oil trains will continue to rumble through cities and towns across the country for years to come, whether or not more pipelines are built.There have been modest improvements in rail safety since Lac-Mégantic. However, major risks remain. A Commission of Inquiry can shed light on many unanswered questions about what went wrong at senior levels of government and industry that led to the worst human and environmental railway tragedy in modern Canadian history; and in doing so lead to policy change essential for improving rail safety and helping to reduce the chances of a recurrence.Former executive director of the Canadian Centre for Policy Alternatives, Bruce Campbell was awarded a Law foundation of Ontario Fellowship for his work on Lac-Mégantic. He spent 2016 as a visiting professor at the University of Ottawa law faculty. He is currently writing a book on the tragedy.