"A number of police officers had guns drawn and were yelling at the boy inside the tram to open the doors," he said. Mr Iliff said a female passenger protested when the boy was pushed against a seat and handcuffed.

"She pointed at them (the police) and yelled something ... but the police were pretty angry as well and sort of pushed her aside," he said. "Once things settled down, they talked to the witnesses, but first of all it was pretty brutal." Mr Iliff said he was initially shocked by the police's actions.

"From their point of view I'm sure they didn't know if he had a gun or whether he was trying to kill people, so I guess it was appropriate, but at the same time, it did seem excessive." Victoria Police were not immediately available for comment.

The boy allegedly drove the new low-floor Citadis tram from its depot in South Melbourne up to 30 kilometres, police said. Detective Senior Constable Barry Hills, of the police transit division, said the boy admitted his obsession with trams during a police interview. "He's a nice lad, he's a good lad. I think his obsession just got the better of him," he said.

Senior Constable Hills said the boy went on a test run on Friday night, stealing a tram from the South Melbourne depot and driving it to Port Melbourne, back to South Melbourne, then back again. It was an escapade reminiscent of Nadia Tass' 1986 film Malcolm, in which an eccentric inventor played by Colin Friels loses his job as a tram driver after a joy ride on the tram tracks.

Last night, the boy allegedly drove out of the depot about 8.50pm and went to Port Melbourne. He then used the tram's directional rod to change the tracks and divert the tram towards Clarendon Street in South Melbourne. Police said he altered the tracks again to travel down Glenferrie Road, where he picked up passengers. Constable Hills said police were alerted to the theft by staff at Yarra Trams' control room about 9.20pm. No passengers called police.

Senior Constable Hills said passengers only became suspicious of the boy, who was wearing a jacket similar to a tram driver's, just before his arrest. "There was a couple of moments when the driver overshot the stops and was confronted by a couple of passengers, and that's when they've become a little wary."

Three sets of keys are needed to operate the Citadis trams. Senior Constable Hills said the keys were believed to have been stolen three weeks ago from the Box Hill depot, but said the theft was not reported.

"It does take considerable effort, time and concentration to drive these trams." Senior Constable Hills said the 15-year-old used the test run on Friday night to work out how to use the complicated braking system.

He rejected suggestions the boy may have been taught about trams by well-meaning drivers, believing he learned simply by observing the drivers at work. Although he stressed the potential serious consequences of the theft, Senior Constable Hills said the boy should not abandon his dream of being a tram driver.

"I believe that if he stays on the straight and narrow then it's certainly not going to affect his future," he said. The boy, from Sunshine, was taken to Boroondara police station and charged with nine offences, including two counts each of theft of trams and conduct endangering life. He was bailed to appear before the Melbourne Children's Court on June 20.