Nicola Sturgeon has admitted Scotland’s system of notifying crime victims about their attackers being freed from prison is “not good enough” after it emerged fewer than one in 100 receive advance warning.

Douglas Ross, the Scottish Tory leader, said official figures obtained under the Freedom of Information Act showed the victims of only 37 out of 4,500 criminals serving sentences of 18 months or more had been informed of the proposed release date.

Speaking on International Day for the Elimination of Violence against Women, he told MSPs that the justice system was “stacked against victims” as they were “routinely left in the dark”. He also accused Ms Sturgeon of breaking a promise to the family of Michelle Stewart.

Since the 17-year-old was killed in Ayrshire in 2008, her family have been campaigning for improvements to the victim notification scheme so families are given details of an offender’s release from prison.

Mr Ross said Humza Yousaf, the former justice secretary and now Health Secretary, had promised them a scheme would be “up and running” by this month.

Ms Sturgeon promised to write to the Scottish Tory leader with answers on the progress being made, but did not appear to know what had happened to Michelle’s Law.

The exchanges at Holyrood occurred after three people appeared in court charged with the murder of schoolgirl Caroline Glachan more than 25 years ago.