NEW DELHI, December 1: Three persons accused in a murder case were sentenced to life imprisonment by a city court today. The three accused - Inderjeet Singh, Amar Singh and Shiv Charan - were arrested eight years ago for murdering Devender Singh, who had allegedly killed Inderjeet's father.Additional Sessions Judge S. Gaur said: ``Prosecution has proved case beyond reasonable doubt. All three are convicted under common intention to commit a murder.''Inderjeet Singh, who was also arrested under the Arms Act, will undergo a concurrent imprisonment of one year.On August 3, 1990, Devender Singh was attacked with hockey sticks and a knife when he was returning home from his mother's residence in Arjun Nagar. He was declared dead at the All India Institute of Medical Sciences.A statement by his brother Parminder Singh, who was with him during the attack, led to the opening of a murder case and the arrest of Inderjeet, Amar Singh and Shiv Charan. According to Parminder Singh's statement, his brother had been arrested for the murder of Inderjeet's father three years ago. Devinder Singh was released on interim bail after 11 months of custody in this case.The judge refused to discard the case on the grounds that Parminder Singh's FIR was registered late, adding that the ``motive is proved''. During the trial, twenty seven prosecution witnesses were examined.``The cause of death is the result of shock due to multiple ante-mortem injuries produced by a sharp weapon,'' the court observed.