A former partner of Rebecca Shuttleworth, the mother convicted of beating her son Keanu Williams to death, has been jailed for at least 29 years after admitting murdering a new girlfriend and her baby.

Wesley Williams "executed" care home worker Yvonne Walsh and her seven-month-old son Harrison, possibly, police believe, after she broke up with him because of his chequered past.

Williams, 29, used a ligature to murder Walsh, 25, and her son at her home in Birmingham and left their bodies lying on their beds. Later he took to social network sites to hint at what he had done before telling the police.

Sentencing him on Wednesday Mr Justice MacDuff said Williams was "evil and dangerous beyond measure". The judge said: "You decided to kill her, in fact to execute her. It was your decision that she had to die. Then you killed Harrison as well, probably as he lay in his cot. The casual way in which you did this was chilling.

"The agony, physical and mental, which she [Walsh] must have gone through in the final conscious minutes of her life, is almost unimaginable as she realised what you were doing and that she was powerless to stop you."

Birmingham crown court heard that Williams had recently come out of prison and a few days before he murdered Walsh and Harrison he was informed that social services would need to check in on them. One theory held by investigators is that he had been planning to propose to Walsh but she broke up with him after he told her about his past.

The double murder took place in May as Rebecca Shuttleworth, 25, stood trial for the murder of Keanu. In June she was jailed for life and told she would serve at least 18 years before she could be considered for parole.

The case of Keanu Williams, who was killed in January 2011, led to a damning serious case review with doctors, social workers, police and nursery staff in Birmingham being accused of missing chances to save him.

It prompted the city council to admit it could not guarantee that the most vulnerable children were safe and caused the government to threaten to take over children's services in England's second city.

Birmingham city council has made it clear that it hadn't been aware of Harrison but the city's safeguarding children board described the murder of mother and son as a "tragic and complex" case and said an independent review would be commissioned. Though they share the same surname, Keanu was not Williams's son.

Peter Grieves-Smith, prosecuting, told the court that Williams had a string of previous convictions for violence including attacking his sister's ex partner with a hammer. Within minutes of murdering Walsh and her son on 31 May, Williams wrote on Facebook: "Sometimes you just have to do things you should not". He changed his relationship status to single and posted on Walsh's page: "I am sorry it had to come to this".

Officers broke into Walsh's home in Billesley, Birmingham, on 2 June and found the woman, dressed in pyjamas, in her bed and Harrison next door in his cot. It is unclear if Walsh, who has another child, was killed before or after her son. Williams was arrested at his house in Oldbury.

Speaking outside court, Walsh's brother, Chris Walsh, said: "Yvonne was so joyful, she was the centre of attention because she was always so happy and such a doting mum. She loved her kids wholeheartedly."