Communication failures at Central Region police meant criminal intelligence reports were not considered when 43-year-old Hamilton applied for the seventh time to have his firearms certificate renewed in February 1995.
Lord Cullen's inquiry into the Dunblane massacre heard this week that a computer search by Central police's criminal intelligence unit in January 1995 revealed no record of Hamilton. Old paper files were not checked.
Yet for more than a decade serious concerns about Hamilton's boys' clubs had been made known to police. Central police were also in possession of at least four investigations about Hamilton which had been referred to the fiscals in Dumbarton and Stirling. Warning signs of his irrational behaviour, evident in the vendettas he pursued against the Scouts Association, the local authority and the police, were also not picked up.
The inquiry was also told that Central police's interpretation of gun licensing laws contributed to Hamilton being granted certificates for up to six weapons and more than 7,500 rounds of ammunition.
As early as 1981 secret reports on Hamilton had been made to criminal intelligence. Constable Donald Woolhead, based at Falkirk, submitted three reports over a period of 14 years. The first in 1981 raised concerns about the Dunblane Rovers group for boys, set up after the killer was kicked out of the Scouts Association.
PC Woolhead, who was involved with the Bannockburn Scouts, said: "I knew Thomas Hamilton had left the Scouts under a cloud. I disliked him. I did not like what I had heard about the Rovers group or its activities."
He said he was also worried about boys' clubs Hamilton launched in Stirling and submitted a report about school lets in the area. On January 25 1995 he made his final submission voicing serious concerns about a club in Alloa where Hamilton had taken photographs of semi-naked boys by persuading them that their pictures would be sent on to professional football scouts.
This report did not show up in criminal intelligence records when WPC Anne Anderson, working in the firearms department, asked for background on Hamilton in late January. Even a request to check the computer again in early February, drew a blank. Constable Douglas Hamilton, who carried out the computer search, could offer the inquiry no explanation as to why the report was missing from computer files a month before the licence was renewed, but he admitted it did reappear later.
Perhaps most significantly, a 1991 memo from chief inspector Paul Hughes, (then a detective sergeant) urging his superiors to revoke Hamilton's gun licence, was not only recommended for "no action" by detective superintendent John Millar and deputy chief constable Douglas McMurdo, but was absent from the killer's firearms file in 1995.
Hughes's plea had been made after extensive investigations into Hamilton's Loch Lomond camp in 1991 in which one boy was physically assaulted three times by Hamilton who had "lost control".
The inquiry was told about a number of other reports which may have had a bearing, which were missing when firearms officers asked for background.
One in June 1988 expressed suspicions about Hamilton's Falkirk Boys Sports Club, and another by Alva primary school board member Elizabeth Watt warned the police in 1995 that Hamilton had made videos of scantily clad youngsters at his gym club in Clackmannanshire.
To add to the confusion, during 1995 computer files were temporarily wiped from police archives by a computer error which went unnoticed between July and December. Suspicions about Hamilton were further concealed by a two-part computerisation of Central's criminal intelligence records ending in 1993, during which the haphazard transfer of information meant vital reports about the killer held on paper files were wiped or lost. Consequently a file on Hamilton clearly marked "HOMO INDCH" - meaning homosexual, indecency with children - was not seen by firearms officers.
The evidence of Central chief inspector Colin Mather, who dealt with Hamilton's firearms application in 1995, spotlighted shortcomings in Central police's checking procedures under the gun laws.
Mr Mather said that applicants had to give a "good reason" for holding firearms, but submissions as vague as "for target practice and competitions" or simply that they were a member of a gun club, were acceptable. Mr Mather said his final decision on Hamilton was influenced by the approval of the then commander of operations in Stirling, superintendent (now chief superintendent) Jim Moffat.
Earlier the inquiry heard from an anonymous mother who withdrew her son from Hamilton's boys' club at Stirling high school and later received threatening letters from Hamilton, the last just weeks before he massacred 16 children and their teacher at Dunblane primary on March 13, prior to turning the gun on himself.