On three consecutive days last month, about $150 went missing from schoolbags, which students must store in the hat room during recess. Harry was a victim - he lost $18 - and other students had cash and bus passes nicked. Harry, 11, sprang into action.

"The teachers said 'wait, wait, wait' and they weren't taking any action," he said. "I decided to act because I was annoyed that they had robbed a lot of classes, and a lot of people were missing $20." Harry drew on know-how acquired from hours spent glued to the History Channel, his favourite program being a documentary about Vietcong-made traps in the Vietnam War.

On the fourth day, he placed a mouse trap with a $5 note attached in his school bag during recess. He had squirted the device's main bar and metal fittings with green food colouring, cutting a small hole in the note and securing it on the bait hook with sticky tape, so that the thief would have to wrestle with it, thereby setting off the spring and getting hit with the coloured bar.

To his surprise, the thieves took the bait and - after he spread the word among classmates - a witch-hunt began. "I thought 'Oh my God, I might catch these guys'," Harry said. "Everybody was running around seeing who had green on their fingers." One of the offenders was caught green-handed en route to the bathroom in a desperate bid to wash off the evidence. The younger boy confessed his guilt. An accomplice in the same year was also nabbed.

The pair had amassed a booty of $165 from their crime spree - blowing $15 on lollies at the canteen. Harry's mother, Michaela, 38, a nurse, could not be more proud of her son. She said she had grown up around mousetraps and did not believe any child could have been seriously injured. "Harry has a strong concept of fairness and didn't want to see anyone else lose their money," Mrs Cordaiy said. "Initially, the vice-principal had to say it was a little extreme and we don't condone it - but privately teachers were, like, 'Good on you, mate'.

"[The offenders] probably just didn't realise how much trouble they'd really caused. This is the northern beaches, for God's sake. Nobody is that poor." When he's not busy fighting crime, Harry plays rugby union and league and dreams of putting his technical skills to use as an engineer. He has been voted in as a school leader next year. Principal Rob Richmond said the two students involved in taking the money had been disciplined.