A man has been arrested on suspicion of murder after three men in their 80s – two of whom were believed to have been twins – were found dead.
The bodies of two 84-year-olds, named locally as Dick and Roger Carter, were found in Exeter on Tuesday, a day after that of another man aged 80.
Police said the level of violence used against all three had led them to link the deaths.
A 27-year-old man remains in police custody.
Officers were first called to Bonhay Road at 15:00 GMT on Monday, where they found the body of the 80-year-old man.
At 13:00 on Tuesday, police attended a property in Cowick Lane, about 1.5 miles (2.4km) away, and discovered the bodies of the two other men.
Det Chief Insp Roy Linden, from the major crime investigation team, said: “At this time there are several and significant common factors between the two addresses.
“In terms of the level of violence used we decided last night to link the investigations – originally they were treated as two separate murder investigations.”
However, Supt Matt Lawler said officers were yet to establish a “clear connection between the parties involved”.
Dick and Roger Carter were born in September 1934, and were both directors of an agricultural company called Traycrop from the early 1990s until it was dissolved in 2004.
“You had a job to tell them apart they looked so similar, even at their age,” said one neighbour who did not want to be named.
Local shopkeeper Jim Wright, of Broadway Stores, said they were “eccentric” and “reclusive”.
“Richard would come into the shop – I don’t know the other one, he never came in.”
Mr Wright’s wife Kerry said: “It’s horrible to think something like that could happen outside your front door – your house is meant to be your safe place.”
A police cordon was set up at the house, and a small collection of floral tributes could be seen outside.
Windows of the large house were covered in what appeared to be whitewash and strips of tape.
Supt Lawler said the force’s local neighbourhood team would be visiting nearby residents over the next few days to provide “advice, support, and to answer questions”.
He also urged people to check on their elderly neighbours, adding it was an opportunity for the community to “come together”.
Police have so far been unable to trace the family of the man found in Bonhay Road.
A neighbour said he was a “very quiet man who kept himself to himself”.
Shirley Sharpe said she did not know the man personally, but he had lived in the house for “a good few years”.
Supt Lawler said he understood news of the deaths would “cause significant and understandable concern and is an unprecedented event in our city which has shocked us all”.
He added: “I know that everyone’s immediate thoughts will be with the family and friends of these gentlemen, and as you would expect, we are providing as much support as we can to them.”
Both roads will remain cordoned off for the rest of the day, Devon and Cornwall Police said.
The force has appealed for any potential witnesses from either area between 08:00 on Sunday and 13:00 on Tuesday to contact them.
Police added it was “important to avoid speculation” during the “complex case”.