Seven years after remaining behind bars in Nepal for the alleged murder of an American tourist, Nepali courts had rejected Sobhraj's 'not guilty' plea on Jul 30.
Nepal had taken Sobhraj's passport by applying immigration law in 1975 but the law had been implemented in the country in 1990s.
"No one shall be held guilty of any criminal offence on account of any act which did not constitute a criminal offence in the time when it was committed," said UN committee.
According to the UN agency, the trial was heavily biased against Sobhraj.
It also added, "most hearings were cancelled or postponed at the last minute without reasons being provided. The length of proceedings and high number of postponements and cancellations can't be justified."
"Right of access to courts and tribunals and equality before them must be available to all individuals, regardless of nationality and status," said UN.