The AFL boss broke his silnce on the growing scandal at Essendon with an Australian Sports Anti-Doping Authority investigation into possible use of illegal performance enhancing substances.
Demetriou maintained his stand that Essendon chairman David Evans contacted league authorities after Bombers officials were alerted to possible use of illegal drugs in their highly controversial training program last year.
Demetriou denied the league had acted with Essendon ahead of explosive announcements from Canberra on Thursday that the Federal Government will significantly expand authority to investigate use of illegal drugs in sport, as well as extended investigative powers in a bid to curb match-fixing and betting rorts.
Demetriou was in Canberra on Thursday for the release of the ACC report into the integrity of Australian sport and the relationship between professional sporting bodies, prohibited substances and organised crime.
Release of the report and announcements of substantially broader scope for official law enforement agencies to investigate irregularities came just two days after Essendon's stunning confession and call for ASADA to conduct a full inquiry.
Essendon players face automatic two-year playing bans if found guilty and senior club staff including coach and Bombers playing legend James Hird could be de-registered.
"The Essendon story came about because the football club approached the AFL in recent days and asked the AFL and ASADA to conduct an investigation," Demetriou explained.
"They were being asked certain questions by people, including the media, and the (Essendon) chairman took it upon himself to ask various people around the club and then came to the AFL."
Demetriou said the AFL had set up its own integrity unit in 2008, believing at the time the greatest threats to the sport were gambling, performance-enhancing drugs and salary cap compliance.
"As time has gone by we have taken the opportunity for much more intelligence gathering - and with that intelligence gathering and information sharing that's already in existence we've tackled a number of issues," said Demetriou.
"The latest was in relation to the issue of betting. With the issue of performance-enhancing drugs, we were made privy to (it) by the Australian Crime Commission.
"It came as a shock as we have a very thorough and rigorous testing regime.
"But when you hear about organised crime and the sophisticated organisation of drugs and how the scientists are ahead of the testers, then you do have to rely on intelligence gathering.
"But we can do more."
Demetriou said the AFL fully supported the recommended actions and protocols arising from the ACC report.
Additional reporting from AAP