Truscott was the last known person to have seen the murdered girl alive.
Within two days, police charged the teenager with her murder on the basis of purely circumstantial evidence. After a trial that lasted only 15 days, he was found guilty and sentenced to be hanged.
Three decades later, Truscott remembered those days in a jail cell in Goderich, Ont., when he feared he would feel the noose before his 15th birthday.
"I woke up one day and somebody was building something outside the wall," he told The Fifth Estate.
"You could hear the hammering, and I thought they were building a scaffold. And it's just kind of living in terror, and every day you expect it to be your last."
Truscott's sentence was commuted to life imprisonment and he spent the next 10 years behind bars. and he spent the next 10 years behind bars.
The case immediately provoked controversy, not only because of Truscott's tender years but also because some doubted his guilt. The controversy lead to a Supreme Court review
In the spring of 1966, a book written by Isabel LeBourdais – The Trial of Steven Truscott – attacked the rapid police investigation and trial, calling into question a justice system that many people then considered infallible.
Her argument that the court had erred and sentenced an innocent teen to death made front-page headlines and sparked public demonstrations. The resulting uproar in Parliament led Lester Pearson's Liberal government to order a Supreme Court review.
Canada's top court examined the Truscott case in 1966, not to determine his guilt or innocence but to decide whether he should have a new trial. The judges ruled 8-1 to uphold the verdict.
While Truscott remained in prison for three more years, many experts believe the controversy over his case led to Canada abolishing the death penalty in 1976.
Meanwhile, Truscott adopted a new name and settled in Guelph, Ont., where he worked as a millwright, married and raised three children.
Although the Truscott name was well known in Canada, he remained anonymous until March of 2000, when the CBC's The Fifth Estate broadcast a documentary about his case.
The program presented new evidence that, when added to that uncovered by LeBourdais and others since the original trial, built a case that police may have laid charges too quickly, while playing down some witnesses and ignoring other potential suspects.
Truscott said he dropped Harper off at a highway, then saw her hop into a strange car as he pedalled away. He said Harper, the daughter of an officer on the Clinton base, told him she had squabbled with her parents and planned to hitch a ride somewhere.
The police maintained that Truscott killed her before reaching the highway and left her nearly naked corpse in the woods.
Their case, built on purely circumstantial evidence, hinged on the testimony of a pathologist who testified that Harper died between 7:00 and 7:45 p.m. – an extremely precise determination even by today's forensic standards.
In 1966, Penistan had second thoughts and published a review of his autopsy that opened the time frame to a 12-hour window.
The Fifth Estate found that police also dismissed testimony from witnesses, including some who insisted they saw Harper and Truscott reach the highway.
Other suspects ignored?
The police and military never seriously considered other suspects that should have been flagged, The Fifth Estate said. For example, the journalists uncovered old military files on Alexander Kalichuk, a heavy drinker with a history of sexual offences who lived within a 20-minute drive of the base. The air force sergeant had come to police attention after trying to lure a 10-year-old girl into his car about three weeks before Harper disappeared.
