In a chilling letter to former Central Regional councillor Dr Robert Ball, which began “Dear Bob”, the killer wrote: “At Dunblane primary school where teachers have contaminated all of the older boys with this poison, even former cleaners and dinner ladies have been told by teachers . . . that I am a pervert.”

After also criticising Bannockburn primary, another school in the Stirling area, for spreading similar rumours, Hamilton went on: “All of this has been extremely damaging over the years not only to my clubs but to my public standing and has resulted in a complete loss of my ability to earn a living. ”

Dr Ball had endured years of correspondence with Hamilton after supporting his successful complaint against Central Region council to the local government ombudsman, Eric Gillett, in 1983.

The council suspended Hamilton’s letting arrangement for premises at Dunblane high school amid parents’ and teachers’ complaints about his methods, but the damning ombudsman’s report in 1984 ruled the council had acted on “unsubstantiated rumours” alone.

In the years that followed, suspicious education chiefs across central Scotland tried to block 43-year-old Hamilton from holding his boys’ gym clubs on school premises. But because of the ombudsman’s decision, he was able to open clubs across the region and into Lothian and Fife.

In 1989 Lothian successfully suspended his let at Linlithgow Academy, pending the outcome of a police investigation into complaints about a 1988 camp at Inchmoan Island, and was not challenged by the ombudsman.

In 1992 Fife successfully followed in Lothian’s footsteps after three boys, dressed only in their pyjamas, ran away from a camp at Dunblane high school in the middle of the night.

But Central, unaware of the success of the other two councils, continued to look for “too much proof” because of the ombudsman’s 1984 decision and Hamilton was allowed to run his clubs unchecked.

Earlier the inquiry heard that police and social workers had damning testimonies from children who had attended one of Hamilton’s military-style summer camps at Loch Lomond, four years before the Dunblane tragedy.

In one statement about Hamilton’s camp at Millarochy Bay in 1991, when the killer was videoing his semi-naked young charges, a boy described how Hamilton forced another boy to lie in the freezing loch as a punishment. A police investigation followed, but the procurator fiscal did not press charges. A memo from the senior investigating officer, urging his superiors to revoke Hamilton’s gun licence, was stamped “no action”.

Hamilton appears to have given almost everyone he came into contact with plenty of clues about his motives in mixing with young boys and his unsuitability to handle guns. Countless police officers, teachers, council officials, parents and MPs have spoken of their “gut feeling” about him. But time and again “lack of hard evidence” has meant no action was taken.

In a week which has largely concentrated on school-letting policy, the inquiry has spotlighted the conflicting demands of civil liberties and the need to protect children.

It is emerging that Hamilton was clearly an obsessive, but he was also dangerously astute at playing cat and mouse with the authorities, and was able to con people into supporting him, including for a time, Scottish Secretary Michael Forsyth.

He emerged unscathed from four police investigations and at one point labelled Central Police “village idiots”. And he was considered trustworthy enough to have his gun licence renewed seven times.

Whenever any complaint was made against him, he adopted the tactic of bombarding the authorities concerned with letters and official complaints. On five occasions he took three councils, Fife, Lothian and Central, to the local government ombudsman. Only his first complaint, against Central, was upheld, with far-reaching effects.