A 21-year-old has been arrested on suspicion of murder after a man was found suffering from stab wounds at his flat.
The 40-year-old victim, who lived alone, was found in the property in Norfolk Square, Brighton, at 7.40pm yesterday, Sussex Police said.
He received treatment from paramedics at the scene but was pronounced dead shortly after 9pm, a force spokeswoman said.
A post-mortem examination is expected to take place later today, she added.
Police are in the process of tracing the man's next of kin, who do not live in Sussex.
A knife was recovered in the flat and is being examined to see if it is connected with the death.
The spokeswoman said a 21-year-old man, from Brighton, was arrested at a property in the city on suspicion of murder at 9am today and is currently in custody.
Detective Chief Inspector Nick Sloan, from the Surrey and Sussex Major Crime Team, said: "We do not believe that this was a random attack and we are keen to hear from anyone who was in the Norfolk Square area early yesterday evening, and who saw any suspicious activity."
Anyone with information should call Sussex Police on 101 quoting Operation Broadfield, or Crimestoppers, anonymously, on 0800 555 111.