Detectives made covert recordings of conversations two suspected killers had with family and friends during prison visits, a court heard.
Michael McDougall, 47, and Michael Mullen, 24, are accused of murdering Tipu Sultan, who was shot at his takeaway in South Shields last April.
Prosecutors claim Mullen was the rider who took gunman McDougall by motorbike to the Herbs & Spices Kitchen in Lake Avenue to carry out the killing.
Both men are being tried by a jury at Newcastle Crown Court.
Northumbria Police Detective Sgt Joanne Brooks told the court prisoners are notified that their private telephone calls are recorded and monitored.
But the officer told jurors the men accused of killing Mr Sultan were unaware that their conversations during visits were being taped.
She told jurors: "This is a covert tactic."
One recording, of a visit McDougall had with two male friends, was played to jurors yesterday through special headphones.
The court was played a version through loudspeaker but it was too quiet and distorted with background noise to make out what was being said.
Jurors were told the murder of Mr Sultan, 32, from Sunderland, featured on BBC Crimewatch.
Detective Chief Inspector John Bent, who appeared on the programme, told the court the episode featured a reconstruction of the killing.
As a result of the show, a person seen walking passed the shop, who was being sought by police, was traced and eliminated from the inquiry.
But a Ford Fiesta, believed to contain two people, which appeared on the programme, has never been tracked down or identified.
Christopher Knox, defending, McDougall, asked the detective: "The suggestion in the programme was, it was your impression, it had passed (the shop) at least twice.
"It appeared to go past slowly, might have been supervising."
DCI Bent confirmed that the car was being sought but has never been found.
McDougall, of Hylton Avenue, and Mullen, of Hawthorne Avenue, both South Shields, both deny murder, manslaughter and possessing a firearm.
McDougall denies an additional charge of possession of a firearm and Mullen denies perverting the course of justice.
The trial continues.