Police investigating the deaths of two men at separate flats in the same block today urged anyone with information to contact them.
Officers found the first body last weekend when a murder probe was launched. A man was arrested on suspicion of murder yesterday morning, then a second body was found in a separate flat in the same block.
Police have yet to confirm whether the two deaths are connected.
A Derbyshire Police spokesman said officers went to a flat in Waterford Drive, Chaddesden, Derby, at 7.10pm on Sunday after receiving a call about the man who lived there who had not been seen for several days.
When they forced their way in, 66-year-old John Matthews was found dead. After a post-mortem examination, his death was considered suspicious and a murder probe was launched.
Yesterday morning at 6am police from West Cumbria arrested a 47-year-old man in Whitehaven, Cumbria, on suspicion of murder in connection with the inquiry.
He was due to be transferred yesterday to Derbyshire to face questioning.
As part of further inquiries at the flats yesterday morning, officers found a second body in a separate flat, believed to be a man in his 50s, at about 9.10am.
"His death is being treated as suspicious but police are not able to confirm at this stage if the two deaths are connected," the spokesman said.
"A post-mortem examination will be carried out in due course."
He said police remained at the scene while house-to-house inquiries and forensic examinations continued.
Assistant Chief Constable Steve Cotterill said: "We are still at the early stages of this investigation and we still have many facts and details to establish.
"What I would ask is that if anyone in or around the Waterford Drive area heard or saw anything strange or suspicious in the last week to contact the police.
"I would like to thank local people for their co-operation and patience so far.
"An incident room has been set up and we are putting specialist resources to the inquiry including our Major Crime Unit, Task Force and a high visibility presence from our Safer Neighbourhood teams."