The boy jumped a security fence at the Alice Springs Reptile Center in central Australia early on Wednesday, then went on a 30-minute killing spree, using a rock to slay three lizards, including the zoo's beloved, 20-year-old goanna, which he then fed to 'Terry,' an 3.3 meter, 200 kilogram saltwater crocodile, said zoo director Rex Neindorf.

The boy, whose deadly acts were caught on the zoo's security camera, also threw several live animals to Terry over the two fences surrounding the crocodile's enclosure, at one point climbing over the outer fence to get closer to the giant reptile. In the footage, the boy's face remains largely blank, Mr Neindorf said.

'It was like he was playing a game,' he said.

He killed 13 animals worth around AUS$7,000 (S$7,970), including a turtle, bearded dragons and thorny devil lizards, Mr Neindorf said. Although none were rare, some would be difficult to replace, he said.

'We're horrified that anyone can do this, and saddened by the age of the child,' Mr Neindorf said.

Alice Springs police said they identified the boy, who lives locally, but were unable to press charges because of his age.

Children under age 10 are not criminally liable under the law in the Northern Territory.

'By all accounts, he's quite a nasty 7-year-old,' said Mr Neindorf, who plans to sue the boy's parents. 'If we can't put the blame onto the child, then someone has to accept the responsibility.'

The zoo's security system, which relies on sensors, probably did not detect the boy because he is so small, Mr Neindorf said. -- AP