A man has been jailed for life for murdering his girlfriend's 13-month-old son.
Noah Serra-Morrison was found dead on November 21 2015 after suffering 15 fractures to his body, including a 6in (15cm) wound across his skull.
Mr Justice Jeremy Barker, sitting at Luton Crown Court, described Hardeep Hunjan, 27, as a man with a "volatile nature" who had inflicted a series of assaults on the toddler.
He said Ronnie Tayler-Morrison, 22, had failed in her duty as a mother because she did nothing to stop the attacks by her lover. She was "fixated" with her lover even though he attacked her and was a danger to her son, the judge said.
Medical experts said the toddler's injuries were so severe they were similar to those arising from a car crash or a fall from a building. Noah would have been severely brain-damaged if he had survived.
Hunjan, 27, was sentenced to life for murder with a minimum term of 23 years and two years for child cruelty.
He was also sentenced to 13 years for grievous bodily harm with intent arising from a separate incident where he brutally attacked a vulnerable neighbour, by punching her in the face, swinging her into a wall. He left her with a series of injuries across her face and body.
Tayler-Morrison, 22, who was cleared of murder, was sentenced to six-and-a half years in jail for causing or allowing the death of a child and two years for child cruelty. The sentences are to run concurrently.
The couple, of Crawley Road, Luton, had binged on drink and drugs during Noah's last hours.
The judge told the couple: "I am satisfied that neither of you provided a truthful account of what happened on that night."
The judge told Hunjan that "it remains a mystery why you attacked him" and pointed out that the boy had been unwell in recent days, probably as a result of his fractures.
He said: "At some stage you took hold of Noah. I am satisfied that in addition to punching him to his head you swung him into one of the walls with sufficient force to cause a fracture to his skull and all four of his limbs."
Hunjan and Tayler-Morrison had told paramedics and neighbours that Noah injured himself falling from his cot - a claim which the prosecution told the jury was impossible.
The judge told Tayler-Morrison that she should have know that Hunjan, who has convictions for grievous bodily harm in 2009 and assault occasioning actual bodily harm in 2011, represented a "significant risk" of causing harm to Noah.
He said: "Instead of taking measures to protect your son you continued to expose him to danger and adopted some of the explanations to cover up and continue your relationship with him."
The judge noted that Hunjan was violent towards Tayler-Morrison who had an emotionally unstable personality and showed elements of battered women's syndrome.
He told Tayler-Morrison that she had also failed Noah because of a "selfish aspect of her nature in which you chose to put your own gratification above the interests of Noah."
Telling Tayler-Morrison that she allowed rather than caused her son's death, the judge said: "You were aware that your co-accused had seriously injured your son on the night that he died. You failed to seek medical assistance for a period in excess of three hours by which time Noah had died."
The trial heard Noah was subjected to horrific and deliberate abuse for weeks before he died.
A post-mortem examination revealed that he suffered fractures to an arm and leg around a week before his death, and similar injuries to an arm and leg between four and six weeks before he died - 15 fractures in total, along with bruising over his entire body.
Prosecutor Jane Bickerstaff QC said they were deliberate injuries, consistent with a "road traffic collision or a fall from greater than one storey".
The unemployed couple began living together shortly after Tayler-Morrison separated from Noah's father in July last year.
Their "chaotic" relationship was fuelled by alcohol and cannabis and based on "love, jealousy and control''.
The couple told a health visitor they did not use drugs or alcohol, but jurors were told a video from November 19 showed Tayler-Morrison almost unconscious from using a device that allowed her to smoke three joints at once.
The evening before Noah died the couple again smoked cannabis and downed a full bottle of vodka after putting the toddler to bed.
At 1.45am on November 21, Tayler-Morrison searched the internet for "my baby is hurt'' and "my baby is breathing but not moving".
Half an hour later she phoned her student nurse sister, telling her she had found Noah on the floor after he pulled a fan on to his cot, and that he was "awake and moving, with his eyes open", but "not with it and not crying".
But she did not call an ambulance until almost 3.30am. Hunjan apparently attempted CPR, but Ms Bickerstaff said that if he did so "it was a false and futile attempt, for show".
Paramedics were left waiting at the door, the court was told, and Noah was found on a bedroom floor, cold and with major swelling to the right side of his head, no heartbeat and not breathing.
He was pronounced dead in hospital at 4.10am.
After sentencing, Detective Inspector Fraser Wylie of Bedfordshire Police said: "The sentences passed against this deceitful pair will ensure they are no longer free to live the hedonistic, selfish lifestyle they clearly enjoyed at the expense of Tayler-Morrison's own son.
"Their toxic partnership meant little Noah was never treated with the dignity and love that - as a beautiful, completely dependent baby - he craved and deserved.
"Tragically tiny Noah had his life brutally and mercilessly cut short by Hunjan, as his mother turned a blind eye to the abuse that was repeatedly inflicted upon him."