The lone suspect in the brutal slaying of a 9-year-old boy in Koh Kong province was tracked down to a prison in Thailand on Friday, three months after the investigation into the 2009 killing was reopened.

On December 18, 2009, Sok Phan walked into a busy classroom in Kon Kuk Primary School carrying a large knife and asked Yoeun Pov Rattanak where his father was. The youngster responded that he did not know.

In full view of the class, including his own son, Phan dragged Rattanak outside and slit the child’s throat, before slicing his stomach so deep some of his insides spilled out.

“This is absolutely one of the most horrendous cases we’ve ever dealt with,” said Child Protection Unit (CPU) Director James McCabe. “The level of violence and manner of this crime, to be done in such a public way, is unthinkable.”

While police in Koh Kong quickly established that Phan had launched the attack following a dispute with Rattanak’s father over a boat engine, the case hit a dead end after Phan and his family disappeared from the province.

In June this year, Koh Kong police approached the CPU to help reopen the case and an investigation began that took them through four provinces and into Thailand.

Initially working with the Interior Ministry and Koh Kong police command, the CPU established Task Force Romeo – the 11th multi-agency task force formed in 2015 to investigate serious crimes against children.

Investigators followed a trail of family connections and tip-offs into Kampot, Oddar Meanchey and Preah Vihear, with the police commands of each province joining the task force along the way.

They eventually established that Phan may have been imprisoned in Thailand, but visits to prisons in Surin and Sisaket provinces turned up nothing.

But after investigators in Preah Vihear discovered Phan had changed his name to Yeng Dy, another tip suggested he was imprisoned in Ubon Ratchathani province under his new name.

With the cooperation of Thai security services, on Friday investigators from Task Force Romeo confronted Phan at Ubon Ratchathani Central Prison, where he was sent six months ago to serve a two-year sentence for illegal logging.

According to McCabe, with an Interpol red notice issued once Phan was identified, the extradition process will commence imminently, with Phan facing a life sentence on charges of premeditated murder.

McCabe hopes the success of the investigation will send a message to other serious criminals who remain at large.

“They should be put on notice that their days of freedom are numbered,” he said.

A spokesman for the Interior Ministry could not be contacted for this report.