A sex fiend walked away laughing after attacking a woman from behind, it has been revealed.

The indecent assault took place at around midnight on Sunday, July 23, in an alleyway near Hillcrest Avenue, Silsden.

Keighley police inspector Paul Spencer describes the attack as particularly "nasty."

"The place it happened is where you wouldn't tend to get passing people, which would suggest that it's someone from the area.

"That time of night is not a busy time and so there wouldn't be many people around," says Insp Spencer.

The 37-year-old woman was walking home from a night out in the town when she heard the sound of someone approaching behind her. She was pushed to the floor and fell on to her hands and knees and was assaulted.

Sergeant Allan Gee, of Keighley police, says: "After the assault, the suspect got up and walked calmly away back to Hillcrest Avenue, laughing."

He adds: "We would be very pleased to hear from anyone who could offer any information about this attack.

"Perhaps someone saw a man hanging around this area around that time."

The suspect is described as a white male, around 5ft 6in tall, wearing a dark baseball cap and a white shirt or T-shirt. The attacker's victim said he spoke with a local accent.

Anyone with any information on the attack or the suspect should telephone Crimestoppers on 0800 555111 or Keighley police on 01535 617052.