The man leading a public inquiry into the south Wales E.coli outbreak has pledged to leave "no stone unturned".
Prof Pennington said his inquiry would be 'sensitive' to the families
The 2005 outbreak killed five-year-old Mason Jones, and affected more than 150 others, mainly school children.
Opening the preliminary hearing in Cardiff, Professor Hugh Pennington said the inquiry would be completely independent of all public bodies.
The spread of the 0157 strain between September and December 2005 became the UK's biggest outbreak for a decade.
The inquiry is being chaired by Professor Pennington, emeritus professor of medical microbiology at Aberdeen University, who also led the inquiry into a 1996 Lanarkshire E.coli outbreak, in which 17 people died.
In his opening address at the preliminary hearing on Tuesday, he explained that his inquiry would be "inquisitorial and not adversarial".
"It is a means of seeking out the facts in a way that would not be possible in adversarial proceedings, such as a law suit, in which one party wins and another looses," he said.
'Lessons are learnt'
"Its task is not find in favour of one side or another, nor does it determine civil or criminal liability."
One of the first people to address the hearing was Mark Harvey of Cardiff solicitors Hugh James, representing 37 children from 25 schools, as well as 7 adults affected.
He said: "It's very important for them [the families] that they learn exactly how this outbreak occurred, and that lessons are learnt."
A number of representatives of public bodies addressed the hearing, pledging full commitment to the investigation and their cooperation with any aspect of the inquiry.
A minute's silence was held in memory of Mason Jones
These included representatives of four local authorities areas - Bridgend, Rhondda Cynon Taf, Merthyr Tydfil and Caerphilly - which were affected by the outbreak.
Speaking after the initial hearing, Prof Pennington said he had been "shocked" at the size of the outbreak but would not have undertaken the inquiry if he was not convinced he could get to the source.
"I know E.coli pretty well, it's been a companion of mine for some time, it's a tricky sort of beast...," he said.
"We cannot allow outbreaks of this scale to happen again."
Prof Pennington said he did not want to do anything with might prejudice the ongoing police inquiry into the death of Mason Jones and, as such, his inquiry's work and procedures would be limited for the time being.
The hearing began with a minute's silence to remember Mason Jones, who lost his life last October.
His mother, Sharon Mills said in a statement: "Mason was robbed of his life and lessons must be learnt.
"Any development which helps us find out how this terrible tragedy happened is welcome, not only by me, but by all the families affected by the e-coli outbreak."
The senior counsel to the inquiry is Jamies Eadie, who was lead counsel to the Bichard Inquiry in to the murders in Soham, Cambridgeshire, of Holly Wells and Jessica Chapman.