A man who tried to force witnesses in his son's murder trial to change their evidence was today jailed for ten years.

Thomas Harrison, 62, was told by a judge that the sentence for his part in the conspiracy was designed to "loosen the grip" he held over people across Teesside and act as a warning to others considering intimidation.

Harrison's accomplice and long-time criminal associate, John 'Buster' Atkinson, 54, was jailed for four years after the judge rejected claims he was the fall guy in the plot.

The pair spent months hatching a plan to ensure Harrison's son Lee was not implicated in the murder of Middlesbrough market trader Kalvant Singh.

Father-of-five Mr Singh, 41, died after being thrown from an upstairs window of a brothel and crack house in August 2001 as a drug-fuelled gang went on the rampage during of a turf war in the town.

Two men were found guilty of murder and jailed for life in 2002, while a third man, who fled to Spain after the killing, was locked up the following year for 18 years for manslaughter. The sentence has since been reduced to 14 years on appeal.

Lee Harrison, 38, also disappeared after the night of violence and was finally traced to Jamaica and brought back to the UK to stand trial last year for Mr Singh's murder.

Harrison, from Middlesbrough, changed his plea to guilty to manslaughter on the day of his trial and he was locked up for nine years.

Teesside Crown Court heard yesterday how Thomas Harrison and Atkinson put pressure on witnesses from the earlier trials to change their evidence which put Lee at the scene of the death.

Atkinson, of Orchard Way, Ormesby, Middlesbrough, paid for one of them to stay in a hotel for two months at a cost of £700. He later altered his statement.

Another witness was captured on CCTV being handed money by Harrison, while damage was also done to a person's home by a gang hired by him, possibly from Leeds.

Atkinson admitted conspiracy to pervert the course of justice, while Harrison, of Ormesby Bank, Middlesbrough, denied the same charge but was found guilty after a trial. He was ordered to pay prosecution costs of £23,433.

The Recorder of Middlesbrough, Judge Peter Fox, QC, praised the witnesses who had the courage to give evidence.

Middlesbrough district commander, Superintendent Mark Braithwaite, who led the investigation, added afterwards: "These sentences close the final chapter to what has been one of the longest-running and most complex investigations carried out by Cleveland Police."

The court heard yesterday how Harrison had a criminal history going back to the late 1950s which included a drugs conspiracy, wounding and dishonesty; while Atkinson's record included blackmail, attempting to pervert the course of justice and assaulting police.

Harrison's barrister, Christopher Knox, said his involvement in the conspiracy was borne out of the belief that his son was innocent, and pointed out that his client had not been convicted for more than 20 years.

Eric Elliott, defending Atkinson, said he was fearful of prison and suffered from a heart complaint and diabetes. .