A special witness has been given immunity from prosecution in return for testimony about how the members of the gang allegedly sought to obstruct the police investigation.

The teenager, who cannot be identified, is expected to be questioned about the gun used to kill Rhys, a .455 Smith and Wesson.

Neil Flewitt, QC, for the prosecution, said that the witness received a mobile phone call from Sean Mercer ordering him to take a taxi to a named address. When he arrived he was given a heavy package that he realised only later was a gun. Sean Mercer is alleged to have told the witness: “Don’t say anything to no one.”

He hid the package in a kennel for the next few days before another alleged conspirator turned up at his home and told him: “I’ve come to move that.” The visitor asked for a bag and then climbed into the loft.

The prosecution alleges that he not only hid the murder weapon but also a converted Walther PK blank cartridge pistol and ammunition.

On September 30 police executed a search warrant. They found both guns in the loft. Mr Flewitt said the witness had entered into an immunity agreement with the Crown Prosecution Service and will not therefore be charged.

He told the jury: “You will have to approach his evidence with caution because it might be suggested that he is giving evidence for the sole purpose of saving his own skin.”

The jury was also told that detectives planted a listening device at the home of James Yates, 20, in Croxteth. He denies supplying the weapon.

Sean Mercer’s friends and associates are accused of taking part in a conspiracy to dispose of the weapon he used, his clothes and his bicycle.

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