A jury has heard that a prison officer at a top security jail emailed a prison governor asking him to have a "quiet word" with a guard who was giving evidence at a series of abuse trials against former officers at Medomsley Detention Centre in County Durham.
John McGee, 50, told Durham Crown Court the email was a "moment of madness" after his father had been convicted for his part in the mistreatment of inmates at Medomsley Detention Centre in the 1970s.
He denies a single count of perverting the course of justice, saying he did not think Phil Husband, the number one governor of Durham Prison, would act on the email he sent.
Deborah Smithies, prosecuting, said an officer called Hugh Cockburn gave evidence at three trials at Teesside Crown Court about seeing young inmates being assaulted in the reception at Medomsley.
He now worked at Durham Prison, where Mr Husband was the boss.
McGee's father, also called John, was convicted of one charge of assault and misconduct in a public office in December 2018, in the second of three trials of ex-guards.
Before the third trial involving three other defendants started, his son, who is a prison officer at the high-security Frankland Prison, emailed Mr Husband with whom he had trained 25 years ago.
McGee junior wrote that Mr Cockburn had been "sticking the boot in" by giving evidence, adding: "If I had my way he would be dealt with if you know what I mean."
The email continued: "Now it's not for me to say anything Phil, but a quiet word in his ear would be a good idea."
McGee junior wrote that his father had been cleared of 12 counts by the jury but convicted of misconduct, describing that verdict as "bloody rubbish".
Miss Smithies said: "This was a bold attempt by John McGee junior to put Mr Cockburn off. In his view, it was wrong for a prison officer to take the side of ex-inmates in the trial of ex-officers. He wanted Mr Cockburn's boss to have a word with him."
Jurors were told Mr Husband went to the police with the email, and McGee was arrested.
The court heard Mr Cockburn did give evidence in the third Medomsley trial.
McGee junior told police in a prepared statement: "I simply wanted Mr Cockburn to understand that he had contributed to putting my family through a difficult time."
The defendant, from Burnopfield, County Durham, told jurors he wrote the email while he was at work with a broken ankle, having gone through the upset of helping his father at his six-week trial and seeing him convicted.
He had not realised Mr Cockburn had not given evidence about his father - with whom the witness had never worked, and that his evidence was about other defendants.
McGee, a father-of-three, said the email was a moment of madness which he should not have sent, adding: "My head was all over the shop. I was emotionally drained by that point."