A police investigation into the wrongful jailing of teenager Lin Qiaoying has found no evidence officials used threats or intimidation to force a confession. The South China Morning Post understands a police report - now with the Department of Justice - will not lead to criminal charges against immigration officers. However, the inquiry identified serious flaws in the way the Immigration Department interviews suspects and presents evidence to courts. The investigation - set up to find out whether officials had attempted to pervert the course of justice - is likely to add urgency to the Ombudsman's inquiry into Qiaoying's case and another controversy involving a traveller also wrongly charged with having a fake passport. Qiaoying, 17, was taken off a New York-bound plane at Chek Lap Kok on October 9 on suspicion she was travelling on a forged passport. She said she was forced to sign a confession and plead guilty to the offence in court after being threatened by officials and told by an interpreter to admit the charge. She served 2.5 months in prison before being acquitted on appeal after her passport was found to be genuine. Investigations in the United States by detectives from the New Territories South Regional Crime Squad have revealed that Qiaoying's mother, Lin Fanghou, has lost her US Green Card five times since the family emigrated from Fujian province to New Jersey in 1995. At least two burglaries have been reported over the same period at the family's restaurants in the US, in which they say their travel documents were stolen. The revelations came after an Immigration Department source said there had been at least five incidents of people using mainland passports belonging to Qiaoying's siblings. The family denies any connection to human smuggling rackets out of the mainland. The probe is also expected to criticise the Judiciary over the use of the same part-time translator - since suspended - both when Qiaoying was arrested and when she appeared in court. In a 48-page statement faxed to the Department of Justice, the girl is understood to have stuck by her allegations. But the source said: 'We have found nothing illegal.' However, the source described the management of procedures in the Immigration Department as 'totally unprofessional'. 'One of the better things that should happen is that there will be a review of their [Immigration Department] procedures. That is where the whole thing fell apart. 'But no one else can add anything to the allegations [Qiaoying] has made,' said the source. Police plan to travel to Fujian to interview a woman intercepted using a forged passport on the same flight as Qiaoying. The former served four months here before being repatriated. Qiaoying told investigators the woman would back her allegations.