Three suspects in the murder of a man whose body was cemented in a box in a Tsuen Wan flat fled for Taiwan nearly three weeks before his decomposing corpse was found. A source with knowledge of the investigation said Hong Kong police had sought help from their Taiwanese counterparts, but the case is complicated by the absence of an extradition treaty between the two sides. Grenville Cross, a former director of public prosecutions, said the lack of a formalised mechanism was a huge obstacle to securing the return of the suspects. “Unless the authorities in Taiwan are prepared to simply expel the suspects, it will be difficult, if not impossible, to secure [their] return,” Cross said. The source said the three left Hong Kong on March 11 – police found the body on March 29. Earlier on Friday police said the victim probably suffocated. An examination had ruled out strangulation because no injuries were found on his neck, according to another source with the knowledge of the investigation. “It is possible he was suffocated as his mouth and nose were covered with something such as quilt,” the source said. “Further tests are needed to find out what he inhaled. Fibres will be collected from his lung and throat and taken for examination.” The victim is thought to be a missing 28-year-old man, Cheung Man-li, as clothes found on the body matched those worn by Cheung. Fingerprint samples had been taken from the body and sent to the Immigration Department to verify his identity. Money dispute suspected: three arrested after police find decomposed body in cement-filled box Cheung was last seen entering the Fui Yiu Kok Street industrial building in Tsuen Wan on March 4. His girlfriend reported him missing two days later. The 26-year-old woman was among five people – three men and two women – arrested on Wednesday for conspiracy to commit murder after the cemented body was uncovered in the ninth-floor flat on Tuesday night. “The woman allegedly told police that she did not know the other suspects, but investigation showed they knew them. Officers suspected her of hiding something,” another source said. In the early hours of Friday, Cheung’s girlfriend and three other suspects were granted police bail. The four are required to report back to police in the middle of the month. The fifth suspect – a man aged 26 who was arrested on Wednesday night – was questioned further on Friday afternoon and then also released on bail. Police are still searching for a 27-year-old man – the flat’s tenant – and his girlfriend. Another man who pushed a trolley loaded with bags of cement into the building on March 4 was also being sought. Police believe Cheung was killed when he went to the flat to demand payment of a HK$1 million debt. The grisly details emerged when officers from Hong Kong Island regional missing persons unit checked Cheung’s phone records and discovered the tenant was one of the last people he had been in contact with. The badly decomposing body was encased in a cement cube that was one metre long, one metre wide and half a metre tall. It took firefighters several hours to crack open the cement. Officers believe the flat was cleaned after the victim was killed inside, but some blood was found on the wall.