The jailed leader of the antigovernment Tiger Head Movement and mastermind of a failed 2009 plot to bomb the Defence Ministry escaped police custody on Saturday after his family fed drugged food to the guards supervising him while he was in hospital, officials said.

Som Ek was in 2010 sentenced to 28 years’ jail for training terrorists and planting two bombs at the state-run TV3 station and one at the Defence Ministry. Two months earlier he had been sentenced to 18 years for a 2007 plot to bomb the Cambodian-Vietnamese Friendship Monument.

He escaped from the Khmer-Soviet Friendship Hospital – where he had been hospitalised for about two days after fainting due to a blood problem – at about 10pm on Saturday, after his two guards fell asleep, said Phin Yan, the chief of PJ prison, where Ek was serving his sentence.

“We assigned two officers to guard him, and according to our officers, they performed according to the procedures, with feet-cuffs on him during night and day, but because they ate food from his family, they lost control and fell unconscious,” Yan said.

“It might have been poisoned food . . . and when they woke up about half an hour later, the prisoner had gone,” he explained. “His feet-cuffs had been taken off and he ran away . . . while they were unconscious.”

One of the guards was positioned at the foot of Ek’s bed and another outside the room, as per procedure, Yan said. Asked why the guards had eaten food offered by Ek’s family, he said they were hungry.

“It was raining and they could not buy food, therefore they ate the food,” he said. “In short, this was because of the carelessness of our officers.”

Sorn Keo, spokesman for the Interior Ministry’s General Department of Prisons, said officials were working with police to recapture Ek, whose group is considered a terrorist organisation by the government. Police officials could not be reached yesterday.

Ek was arrested in January 2009, a few days after the unexploded bombs were found and destroyed by mine clearance workers. He initially confessed to a terrorist plot but later said the confession was forced and that his group were peaceful dissidents.

While the government has said groups like the Tiger Head Movement represent a serious threat to security, there have long been claims it has invented terrorist plots to create a pretext for repression.

Opposition spokesman Yim Sovann in 2009 said he did not believe that the Tiger Head Movement was real, while Prime Minister Hun Sen has more recently been keen to link the group and other alleged terrorist organisations to the political opposition.

“Entire groups have been hiding in the opposition party, and I would like to send a message to the opposition, that when these people are arrested, don’t say they’re just members of the opposition – they are terrorists,” Hun Sen said in a speech in May 2013.

Pang Sokhoeun, a former associate of Ek and himself a dissident who fled Cambodia for Sweden in 2005, said yesterday he met Ek in Thailand prior to the failed plots – when he went by “Chea Sakda” – and that he did not believe the story of Ek’s escape.

“He also told me about his family story – that he had no family in Cambodia, only a wife in Thailand with no child. So, the claim that his family drugged the prison guards is inconsistent with what Sakda told me then,” Sokhoeun explained.

Sokhoeun acknowledged Ek could have family he did not know but said that the former soldier would not have had trouble finding better help.

“According to his background, I am sure he has many friends in the government,” he said.

“To my assumption, it is a political plot so that the CPP can have the upper-hand by allowing him to wage threats against the government . . . and use this pretext to buy more toys, to mobilise forces or prevent the fair and free election to happen if it foresees a loss.

“Or it can use this as a means to tighten security to prevent any protest from the people and opposition in the future against its absolute power.”

At Khmer-Soviet, meanwhile, a private guard for the hospital said he had no sympathy for his counterparts from the prison who had allowed such a basic security breach.

“We heard about the prisoner running away,” the guard said. “This was the guards’ mistake, so they should be detained as prisoners instead of him.”