Four men were being questioned on suspicion of murder after a fatal stabbing.
West Mercia Police said a team of around 50 officers were investigating after a 52-year-old man was found with stab wounds in Shrewsbury, Shropshire, at 6.15pm yesterday.
The unnamed victim was taken to the Royal Shrewsbury Hospital from a flat in Kynaston Road, Harlescott, but was pronounced dead soon after arrival.
Detective Sergeant Jonathan Matthews, who is working on the inquiry, said officers had already received a good response from neighbours and local residents, but believed others may have helpful information.
The detective said: "The man had serious injuries and was taken to the Royal Shrewsbury Hospital, but unfortunately was pronounced dead a short time later.
"A 25-year-old man was arrested at the scene on suspicion of murder. Three other men - two aged 25 and the other 40 - were arrested in the Harlescott area within a few hours."
The four suspects are being held at Monkmoor police station, Shrewsbury, and at Malinsgate police station in Telford.
DS Matthews appealed for anyone with information about the death to contact Shrewsbury police station on 0300 333 3000.
"We particularly want to hear from anyone who heard a disturbance at the flat in Kynaston Road between about 5.45pm and 6.30pm last night, or if they know of any arguments or disturbances at the premises or in the street around Kynaston Road and Lancaster Road involving a number of men during the past week or so.
"It is vitally important to the investigation team that they contact the police without delay."