Police released this composite sketch of a man wanted in a sexual assault in Banff. (RCMP)

A transient man arrested last week in an attack on a woman in Banff is being released because police say they arrested the wrong person.

The charge of sexual assault is being withdrawn against Allen Patrick Slade Viscount, 38, of no fixed address, the RCMP said in a news release on Sunday.

Investigators "uncovered evidence to suggest that this male is not responsible for the attack," the force said.

The victim — a restaurant worker from Australia in her mid-20s — was walking alone in the Alberta mountain town on July 12 after her night shift when a man attacked her. She was sexually assaulted after being beaten in the head and face, police said.

A composite drawing of the suspect, based on information by the victim and a witness, brought in several tips, and resulted in Viscount's arrest and charge on July 13.

The woman's attacker is still at large, police said Sunday. He may still have scratch marks on his face and around his eyes left by the woman. He is described as:

• About 23 to 28 years old.
• Five feet, seven inches tall.
• Stocky build.
• Having a dark, short, crewcut-style haircut and receding hairline.

The woman was treated in hospital for minor physical injuries.

Police repeated on Sunday a warning for people to avoid walking alone at night, to be aware of their surroundings at all times and to stay away from areas which are unlit or isolated.