A tabloid reporter who allegedly bought stories about Jon Venables' life in prison was accused of lying on oath when he told a court he was unaware his anonymous source was a prison officer.
Tom Savage told jurors he never knew Scott Chapman's true identity or that he worked at the prison where Jon Venables served time behind bars for child porn offences.
But under cross examination, prosecutor Jonathan Rees QC questioned him about Chapman's earlier evidence to the Old Bailey that he did not hide the fact he was a prison guard from journalists.
"I'm going to suggest your statement that you were at no point aware he was a prison officer is a lie," Rees said.
"It's a serious thing to lie on oath."
But Savage, 37, maintained that he did not know and had authenticated the man he knew as Adam by the "codeword" of Venables's new name which was not in the public domain.
Towards the end of his dealings with Chapman, "alarm bells" started to ring as stories began fitting into the general news agenda, prompting him to carry out internet searches.
He said: "There was just something not quite right about it so I was just trying to find a bit more without pushing the button. We would not publish information we thought was a lie."
The court heard that 25 notebooks were seized by police following Savage's arrest but none of them contained details of his conversations with Chapman during 2010 and 2011 while he worked at the Daily Star and Daily Star Sunday.
The journalist told jurors he did not learn a great deal of shorthand during his journalism degree due to illness and many of his notebooks would have been shredded or destroyed "to get rid of any confidential information".
Savage, who is originally from Cheshire but now lives in south London, denies conspiring to commit misconduct in a public office along with a News of the World reporter who cannot be named.
Chapman, 42 and his ex-partner Lynn Gaffney, 40, from Corby, Northamptonshire, deny misconduct in a public office.