An 80-year-old man was assaulted and then locked in his house in Manningham in Bradford.
The pensioner was followed to his home on Carlisle Place on Monday morning, where he was attacked and then locked in.
Inspector Sarah Baker of Bradford South CID said: “This was a heartless attack on an elderly member of the community and must have been an extremely frightening experience.
“It is not yet clear what the motive behind this incident was, however we believe he was targeted in the street and passers by may have seen this.
“The suspect is described as being around 6 foot tall, of large build, in his forties or fifties and dressed in a hooded jumper and a white jacket.
“If you have seen this man around the time of the incident or someone matching the description recently in the vicinity, please contact us immediately.
“We have been conducting house-to-house inquiries in the local area and neighbourhood officers have increased their patrols.
“If you believe you have witnessed any part of this incident or have information which could help us trace the individual responsible let us know.”
Anyone with information about the attack, between 10am and 11am on Monday, should call police on 101 or CrimeStoppers anonymously on 0800 555111.