David Edwards, 22, was outraged that his former girlfriend Marina Turvey - who had married another man - refused to acknowledge that Charlene was his child, the court was told. DNA tests after her death proved him right.
After shooting Mrs Turvey, 19, at point-blank range in front of her husband Jonathan, Edwards took the seven-month-old baby to a secluded spot where he placed her face down on the ground and blasted her with a sawn-off shotgun. The court was told that he then covered her with his T-shirt, formed a cross out of twigs and left a note saying: 'Charlene's life was my life - I had the right to take it.'
Edwards, of Luton, Bedfordshire, denies murdering Mrs Turvey and Charlene but admits manslaughter on the grounds of diminished responsibility. The prosecution has not accepted his pleas. He also denies attempting to murder Mr Turvey. All the offences allegedly happened on 30 April.
The court was told that the dead woman had lived with Edwards while Mr Turvey, 24, was in prison. After his release, however, she resumed the relationship with Mr Turvey and it soon became clear that she was pregnant.
The court was told that Edwards approached Mrs Turvey before and after the baby was born 'but she did not want to know'. On the night before the shootings, he sat outside the Turveys' house in Luton and became furious when she went out, leaving Charlene with Mr Turvey.
The trial continues today.