Police have issued an appeal to trace specific witnesses following the death of Heckmond-wike Grammar School student Ahmed Hassan.
The 17-year-old's death followed an incident at Dewsbury railway station on Saturday, December 15.
Police are keen to speak to a couple who had a small child with them and were waiting in the glass waiting room.
The couple were approached by a group of four youths who then got on the 2.01pm train from Dewsbury to Hudders-field. Police also wish to speak to an elderly couple who got on the same train Mr Hassan would have been travelling on, the 2.07pm Newcastle to Manchester Airport service.
Officers believe they may have seen the incident in which Mr Hassan, of Batley, was fatally injured and were possibly jostled by a group of four youths as they were getting on the train.
Anyone with information is urged to contact Dudley Hill police station on (01274) 373600.
Michael Brook, 18, and a 17-year-old youth, who cannot be named, have been charged with Mr Hassan's murder.
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