Armed police were called out after an incident in Huddersfield.
A passer-by spotted a man with what was thought to be a gun walking along a ginnel near a betting shop in Marsh.
But when the gunman saw the witness he jumped back behind a wall and fled.
Armed police were called to the scene late yesterday afternoon but the suspect remains outstanding.
The unusual incident happened in the alleyway beside Coral Bookmakers on Westbourne Road at 5.45pm yesterday.
The witness had been about to enter the betting shop when he saw a mixed race man in his early 20s walking along the alleyway at the side of the shop.
The man was carrying a black handgun.
He is described as 6ft 3in tall, of skinny build, with short dark hair and was wearing a dark blue adidas jacket or similar.
Det Insp Mark Truelove, of Huddersfield CID, said: “We are trying to ascertain the validity of the witness reports.
“We are seeking anyone who may have seen a man matching this description to contact us.”
Anyone with information should contact police on 101.
In unrelated investigations, police would like to speak to the people pictured in the image gallery below. The people pictured in the images may be witnesses as well as suspects. If you recognise anyone, contact police on 101 quoting the reference number on the image caption.
