Singapore's efforts to extradite a suspect in the Holland Village bank heist have hit a snag in Thailand. The Attorney-General's Office in Bangkok has rejected its request for Canadian national David James Roach.

"We denied it because we are not in the position to consider it," said Mr Amnat Chotchai, director-general of the international affairs department at the Attorney General's Office. He did not elaborate on the reasons.

Roach, 27, is accused of robbing the Holland Village branch of Standard Chartered Bank on July 7, by allegedly handing the teller a note which said he had a weapon.

He flew from Singapore to Bangkok on the day of the robbery, but was detained by Thai police three days later. The Thai authorities revoked his right to stay here, and he has been held at Bangkok's immigration detention centre since then.

It is unclear if there are other avenues that would allow Roach to be flown from Bangkok to Singapore to face trial. The two countries have not signed an extradition treaty.

As an immigration offender in Thailand, he would be deported back to Canada if he cannot be extradited. This would mean Singapore would have to pursue the case with Canadian officials. But that could be complicated by the lack of an extradition treaty between the two countries.

Thailand's immigration police chief Nathathorn Prousoontorn said he was waiting for a final decision on the matter, but could not hold Roach for much longer. Thai police are required to deport immigration offenders as soon as it is reasonable to do so.

"The Canadian government wants us to deport him back to Canada," he told The Straits Times. "Immigration (police) can't detain him for a long time. It has been a month. We have to make a decision."

According to Mr Amnat, the Attorney-General's Office was now processing a request by Singapore police to examine the items found on Roach in Thailand. This has not been concluded, he said.

Singapore police, when contacted, said they are still working with the Thai authorities on the matter.

Roach was arrested on July 9 in Bangkok's Boxpackers Hostel after Singapore police alerted their Thai counterparts. Thai police said he was found with 700,000 baht (S$27,000) in cash, as well as a notebook containing a detailed escape plan that included stopovers in Chiang Mai and Dubai. Also in the notebook was the same message found on the note used in the robbery.

While the contents of the note have never been made public, it has been reported by Shin Min Daily News as: "This is a robbery, I have a weapon, give me money, don't call police." The teller handed over $30,000 before alerting the police.

• Additional reporting by Danson Cheong