Police say a man who was with a 48-year-old woman before she was sexually assaulted after she left a concert has come forward.
He is now helping them with enquiries, police said in a statement.
Police are still in the process of identifying the attacker and say the woman left a concert from the Lincoln Events Centre concert in Selwyn near Christchurch at around 6:30pm on Saturday. She was assaulted nearby at around 7:10pm.
"The investigation thus far has further identified people we believe can help us with this enquiry," says Detective Senior Sergeant Anderson.
"Firstly, there is a middle-aged woman who helped the victim on the corner of North Belt and James Street outside the Lincoln Primary School, opposite the church, this lady stayed with the victim until she was collected by a family member."
The woman also lost a heart-shaped gold locket on a gold bracelet during the attack; police are asking anyone who finds it to hand it to them.
Anyone with information can contact Canterbury police on (03) 363 7400.