Police investigating the murder of a man found with stab wounds in the communal hallway of a residential property made an appeal today to trace the weapon used.
The 51-year-old was discovered unconscious and with several stab wounds when police and ambulance workers were called to Elm Grove, Brighton, East Sussex, just after 10am yesterday.
Despite efforts to revive him, he died shortly afterwards.
One man was arrested at the scene and a second was held later in Worthing, West Sussex, both on suspicion of murder.
Sussex Police said one of the men has now been released and is being treated as a "significant witness" to the incident.
Detectives from the force's major crime branch, led by Detective Chief Inspector Trevor Bowles, are carrying out "extensive inquiries" into the circumstances surrounding the man's death.
Mr Bowles said officers "urgently" needed to trace the murder weapon, believed to be a knife.
He said: "We are trying to piece together the events which led to the death of this middle-aged man at 67 Elm Grove. He was stabbed several times in the chest and side of his body.
"We have spoken to a number of witnesses who have assisted us in putting together exactly what happened and why.
"I would urge anyone who saw a confrontation on the doorstep of 67 Elm Grove, Brighton, yesterday to come forward and help us find the killer.
"We urgently need to trace the murder weapon. I believe that a knife has been used to commit this murder. Should anyone find a blood-stained knife, please call us. It is vital that we trace this weapon."
A section of Elm Grove surrounding the property where the man was found was cordoned off by police yesterday along with a cluster of nearby recycling bins.
Forensics officers could be seen coming and going from the terraced property, which is in a popular student area of the city.
Anyone with information about the incident is asked to contact Sussex Police, quoting Operation Odessa, or Crimestoppers, anonymously, on 0800 555 111.