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, a jury heard.
John McGee, 50, from Burnopfield, County Durham, 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 misconduct in a public office in December 2018, in the second of three trials of ex-guards.
The trial continues.