A new documentary has rekindled the controversy, with filmmaker Scott Millwood uncovering evidence strengthening the case that Hean was murdered, but suggesting she may not have been the prime target.
The widow of an establishment dentist, Hean emerged from the Hobart suburb of Sandy Bay to campaign against plans to dam Lake Pedder and drown its stunning 3km-long alpine beach.
At 10.16am on September 8, 1972, Hean set off from Hobart's Cambridge airport in a World War II Tiger Moth bound for Canberra. There the upright lady in her early 60s planned to lobby federal MPs and sky-write "Save Lake Pedder" above the nation's capital.
Hean and pilot Max Price never arrived, their plane disappearing over Tasmania's east coast, their bodies never recovered. Despite some evidence pointing to potential sabotage of the plane, a police investigation went nowhere and authorities rejected calls for a public inquiry.
Five years ago, Millwood, a Tasmanian-born documentary filmmaker, received a package of police files with the message: "Use this for good."
Millwood said the files suggested police had been uninterested in following controversial lines of inquiry, while a subsequent Freedom of Information request raised further questions. To loosen lips further, he made a public offer of $100,000 to anyone with information leading to the truth of Hean's disappearance and began speaking to those who claimed to have relevant knowledge.
The result is inconclusive; Millwood's $100,000 is still in the bank. However, his investigation, filmed as it was conducted, has resulted in a documentary and book, both titled Whatever Happened to Brenda Hean?.
While it makes no final conclusions, the process unearthed new evidence -- including the discovery of the dress that Hean was thought to have been wearing -- and new theories.
"The police files opened up the possibility that Brenda Hean was not just a target for saboteurs but that Max Price might have been," Millwood says. "We're quick to martyrdom in some ways. Conservationists and the environment movement themselves were quick to assume that Brenda Hean was the target for her politics."
While he says that may well be the case, he discovered that Price and Hean had both received death threats before the flight.
Further, he says Price was a womaniser who had been having an affair with his sister-in-law, causing bad blood in the family.
At the same time, Price was in conflict with a business partner and allegations of embezzlement were brewing. "It could be that old-fashioned motives -- love or money -- were at play," he says.
Millwood says police too quickly dismissed the relevance of a break-in at the hangar where the Tiger Moth was kept.
The Berlin-based filmmaker argues that the fact that thousands of Tasmanians believe Hean was the victim of politically motivated murder highlights an undercurrent of violence in the island state. "This is a mirror to Tasmania," he says.
Whatever Happened to Brenda Hean?
An investigation into the mysterious disappearance of Tasmanian environmental campaigner, Brenda Hean.
Brenda Hean, a dentist's wife, was a part of the Hobart establishment. She made a very unlikely environmental activist - but Lake Pedder was one of those very special places. She and a collection of like-minded people took it upon themselves to save the mountain wilderness lake from inundation to form a dam for the Hydro Electric Commission, and in the process founded the first Green political party in the world.
In September 1972, Brenda Hean left Hobart in a tiger moth aircraft being piloted by Max Price. They were flying to Canberra to write 'Save Lake Pedder' across the sky above the Parliament House and to meet with government officials in an attempt to gain federal political support for their campaign. The plane was sighted several times as it made its way across the island but it never reached its destination. Neither the plane nor its passengers were ever seen again.
Thirty-five years of conspiracy theories have surrounded the intriguing story, but in 2003 a secret source gave celebrated documentary film maker Scott Millwood a package, with the advice USE THIS FOR GOOD. In it were the police files detailing the investigation of the case. Scott Millwood has made a documentary based on his attempts to uncover the truth while eye witnesses are still alive. This is the book of that film.