More than 100 police officers from Cleveland and North Yorkshire are involved in a manhunt for James Allen, the man sought over two murders in northeast England.
Police have also revealed that the 35-year-old man from Blackpool knew his first victim, Colin Dunford, 81, from Middlesbrough.
It is unknown if Allen knew his second victim, Julie Davison, 50, from Whitby.
Both victims lived alone and were battered over the head in their homes.
Cleveland police entered a property in Lothian believed to be Allen's residence, but he was not there.
Lee Johnson, from BBC Teesside, said the property is being guarded by a number of police officers.
Temporary Det Chief Supt Gordon Lang, head of crime operations for Cleveland police, said: "There have been a number of sightings of James Allen in both force areas, which are being followed up, and a huge amount of activity has gone on overnight to find him. This is a 24/7 operation that will not stop until we locate and arrest him.
"Allen knew Colin Dunford. He lived next door to him on Leven Street about a year ago, although at this stage we do not believe that he knew Julie Davison.
"We also believe that Allen may have been involved in a number of other offences and these potential links are currently being investigated. He is known to police and he has a history of committing violent offences."
Adeel Baig, 31, a father-of-three who lives three doors down, told the Telegraph: "I got the impression he might be a drug addict.
"The last time I spoke to him was on Sunday - he knocked on my door and he wanted some pots and pans. He said he was doing some cooking for his wife."
Baig said he has had three conversations with Allen, who "seemed like a down-to-earth person".
"I'm quite shocked about what I've been told this morning," he said.
"I thought he was maybe a drug addict or something like that, but because he spoke back politely I thought I'd have a decent conversation with him."