Rapists have been given a licence to assault the mentally handicapped by a recent Legal Department decision to drop a prosecution, parents claimed yesterday. Two hundred parents and their mentally handicapped children from six concern groups demonstrated outside the Attorney-General's offices and called for improved legal protection to ensure the safety of the mentally disadvantaged. The protest followed a decision not to offer any evidence in a case where a 20-year-old woman with a mental age of six years was allegedly raped by one of her colleagues. The prosecution said a decision to drop the charges had been made because they considered the victim would find it too traumatic to give evidence in the High Court. Chairman of the Parents' Association of Pre-school Handicapped Children, Julie Lee Lau Chu-lai, said the impact of the case had been disastrous. 'We are worried about the safety of our kids, not only the girls but the boys as well.' A Legal Department spokesman declined to comment on the protest.