The prisoner, Stewart, is a biological male who identifies as a woman and was jailed for the murder of John Weir in 2013. Stewart has been held in a women's unit since 2016. Police Scotland said a report would be submitted to the procurator fiscal over the incident.
Stewart is thought to be one of two trans women prisoners held in Scotland's female prison estate. The Scottish Prison Service uses a system of individual risk assessments which aims to keep anyone who poses a danger to women out of the female estate. The guidance allows trans women to be housed in a women's prison if they are deemed not to pose an unacceptable risk.
This guidance is being challenged by the campaign group For Women Scotland in a case being considered by judges at the Court of Session. The Supreme Court ruled in April last year that when the term 'woman' is used in the Equality Act it means a biological woman, and 'sex' means biological sex. Stewart was jailed for life after murdering John Weir, 36, by stabbing him 16 times at his home in Bonhill, West Dunbartonshire.
The 38-year-old accused another prisoner of transphobia in a court case last year, but that case was dismissed. The specific nature of the sexual assault charge has not been disclosed, and the identity of the alleged victim remains unknown. The timeline for the procurator fiscal's decision on charges is unclear.