James Allen denies killing Colin Dunford, 81, of Middlesbrough, and Julie Davison, 50, of Whitby, North Yorkshire.
They were found with head injuries in their homes in April.
Mr Allen, 36, admitted to Newcastle Crown Court that he has robbed hotels all his life.
The prosecution say he was motivated by robbery and Robert Smith QC asked him why he had tried to stay in a Whitby hostel for free.
Mr Allen replied: "I did not want to pay for it as I was going to rob the place. I have robbed hotels all my life."
Mr Allen, responding angrily to Mr Smith's questioning, said: "You are a proper crank you are mate. You are in the wrong profession."
He said: "If you can show any substantial bit of evidence I will admit it to you right now.
"Here's your chance, I'm giving you an opportunity, show me one bit of evidence and I will admit it to the press now."
Mr Allen told Mr Smith he had liked Mr Dunford and called him a "decent old bat that lived next door".
But he said Mr Dunford had nothing to steal.
"Why would I kill him when I could go to a shop that has 20 to 30 times more," he said.
Mr Allen also threatened to throw a ring binder of evidence at Mr Smith and said he would show his "dark side".
The trial was adjourned until Friday.
A man accused of murdering two people has told a court he would admit to the killings if he was shown "any substantial bit of evidence".