A baby boy was murdered by his mother's abusive partner, a court heard.
Kane Mitchell, 31, is accused of murdering Teddie Mitchell in the flat where he lived with the boy's mother Lucci Smith in St Neots, Cambridgeshire.
Mitchell is not Teddie's father but was cohabiting with Smith, 29, who had children from a previous relationship, Cambridge Crown Court heard on Tuesday.
Smith is accused of causing or allowing Teddie's death, as she "knew of" Mitchell's "violent disposition" but failed to protect her son.
Teddie sustained injuries on November 1 and died in hospital 10 days later on November 11 2019, aged 12 weeks old, the court heard.
Karim Khalil QC, opening the prosecution case, said that Teddie was "subjected to a violent assault" on November 1.
"He received fatal injuries as a result of being gripped hard, shaken vigorously and having his head struck against a hard surface," said Mr Khalil.
"In the course of that, he suffered rib fractures, fractures to his collar bone and a fractured skull.
"The forces involved gave him serious brain injuries from which he died.
"Lucci Smith was Teddie's natural mother.
"Kane Mitchell was her partner and was at the time fulfilling the role as father to Teddie.
"We say Kane Mitchell killed Teddie.
"Lucci Smith knew of Kane Mitchell's violent disposition and did nothing to protect her baby from him.
"In fact, she ignored violence in the home while others were contacting social services.
Ms Smith is also charged with failing to act once it was obvious that Teddie was very seriously ill.
"She was told directly by a local GP surgery to contact an ambulance."
Mr Khalil said Smith left Teddie alone with Mitchell for around quarter of an hour when she went on the school run on the morning of November 1.
She later told police that when she returned home at around 9am Teddie was not taking his milk, Mr Khalil said.
She made a series of calls to her local surgery and said Teddie made a "high-pitched squeal when he moved" when she took him from his cot, Mr Khalil said.
Smith was asked to bring Teddie into the surgery and was expected to arrive by 2pm, but said she could not take Teddie in until she had done the afternoon school run, he said.
She was urged to "call an ambulance immediately" in a call at around 2.30pm,
Mr Khalil said, but Smith did not dial 999 until just after 3pm.
Neighbours spoke of "regularly hearing screaming and shouting" coming from the flat on previous occasions, Mr Khalil said.
Mitchell is charged with murdering Teddie on November 1 2019.
Smith is charged with causing or allowing the death of a child on the same date, and of cruelty to a child, by not calling for an ambulance sooner.
Both defendants are jointly charged with causing or allowing serious harm to a child between August 16 2019, the day Teddie was born, and October 31.
This concerns alleged "occasion or occasions" of historical violence against Teddie.
The two defendants deny all the charges.
The trial continues.