A third person is due in court today charged in connection with the murder of a policeman in Northern Ireland.

The 21-year-old man, who will appear at Lisburn Magistrates' Court, is charged with withholding information about the shooting of Constable Stephen Carroll, 48, in Craigavon earlier this month.

A 17-year-old youth and former Sinn Fein Craigavon councillor Brendan McConville, 37, have already been charged with the officer's murder.

Meanwhile, a top republican being questioned about the killing of two British soldiers in Antrim two days before the policeman's murder remained in custody overnight after being dramatically re-arrested yesterday less than an hour after a High Court judge ruled his detention unlawful.

Colin Duffy, 41, from Lurgan, Co Armagh, was one of six suspected dissident republicans whose lawyers challenged a court order granting detectives more time to quiz them.

Duffy and three other were being quizzed about the murders of Sappers Mark Quinsey, 23, and Patrick Azimkar, 21, outside Antrim's Massereene barracks, while the other two were being interrogated about Pc Carroll's death.

The six suspects, who had been held since March 14, applied for a judicial review on a judge's decision to grant detectives a further seven days to question them.

Under UK anti-terrorism laws police can hold terror suspects for up to 28 days without charge.

But Northern Ireland Lord Chief Justice Sir Brian Kerr yesterday quashed the extension on a legal technicality.

He said county court judge Corinne Philpott, while making her deliberations, had not taken into account whether the suspects' original arrest had been lawful.

Sir Brian did not question the lawfulness of those arrests but said Ms Philpott should have examined the issue.

On that basis he upheld the defence team's claim that the decision should be reversed.

But no sooner had Duffy been released in the wake of the judgment than he was taken back into custody to face fresh police questions.

His lawyers and family protested bitterly about the re-arrest but police stood by the decision to keep him in custody as their investigations into the killings continued.

Duffy was once cleared of the IRA murders of a soldier and two police officers who were gunned down in separate attacks in 1993 and 1997.

In relation to Pc Carroll's murder, McConville, from Glenholme Avenue, Lurgan, was remanded in custody yesterday, 24 hours after the teenager appeared in the dock.

During their respective hearings, police told the court that McConville had denied killing the policeman while the youth had refused to answer any police questions despite being interviewed almost 20 times.