The engineer who was arrested on suspicion of plotting a series of bomb blasts in Rangoon in April has been denied legal representation, his lawyer said.

Kyaw Ho, the lawyer of Phyo Wei Aung, said that his client should, under domestic law, be released having been held for a month without charge.

Phyo Wei Aung is accused of being behind three separate attacks on the X20 pavilion in Rangoon on 15 April, as revellers celebrated the annual water festival. Nine people were killed and dozens injured. He was arrested by police on 23 April.

His lawyer said that he returned to court on 20 May to again request permission to represent Phyo Wei Aung, but was told that “it has not yet been approved”. It is the third time he has requested permission.

“So according to the law, if they cannot press [charges] on 23 May, then he has to be released. That’s what we have to wait for and see. Maybe that’s why they are not granting [legal representation].”

Phyo Wei Aung is accused by the government of being a member of the Vigorous Burmese Student Warriors, stormed the Burmese embassy in Bangkok in 1999 and took 38 hostages.

Police said that three grenades had been thrown into the crowds during the water festival. Another device, made with a beer can filled with explosive powder and attached by detonation wire to a mobile telephone, failed to explode.

A Rangoon-based graphic designer and his son were arrested after taking photos of the aftermath of the bombing, and are still being held.

Yee Yee Tint, the mother Sithu Zeya, said that her son had been tortured and denied food during his detention. He and his father have been charged under the Unlawful Associations Act.