Detectives are searching for a man who phoned Essex Police anonymously the night a 24-year-old was fatally stabbed in Braintree.
The man phoned, without giving his name or details, from the phone box in Mountbatten Road, near to the Co-op store and Swiss Bell Public house, in the evening of April 16.
He provided information which police now believe could be linked to this investigation into the murder of Michael Haastrup.
Senior Investigating officer DCI Mark Hall said: "We need this man to contact us urgently as he may hold vital information.
"We can assure him that his phone call will be treated in the strictest confidence.”
Anyone with information should contact the Brentwood Major Investigation team on 01277 266869 or via 101 or through Crimestoppers on 0800 555 111.
Luke Eva, aged 24, from Leigh on Sea has been charged with the murder of Mr Haastrup and is remanded prior to a trial hearing.
A plea and case management hearing is scheduled for June 23.