THE man who has admitted that he killed 18-week-old Isabella Vallance often got drunk and was violent towards the mother, Worcester Crown Court was told.
Tyler Vallance suffered from ADHD and behaved perfectly normally when he took his medication.
But sometimes he turned nasty when in a jealous mood and ill-treated his partner, Jessica Wiggins, it is alleged.
Her best friend, 18-year-old Drew Whyley, told the jury on the fourth day of the trial that she had seen marks on Jessica's neck and arm where he had grabbed her.
Vallance, aged 21, of Engadine Road, The Oakalls, Bromsgrove, has pleaded guilty to manslaughter. Wiggins, aged 19, of Heathfield Road, Redditch, is on trial for charges alleging that she failed to protect her child.
Miss Whyley said she knew Jessica from college days when they used to hang around together.
She learned of Jessica's boyfriend and initially thought he was "bubbly and fun". But later she described him as "unpredictable, angry, violent and sometimes threatening".
When she visited the couple in their rented flat in Stanley Close, Redditch, she noticed Vallance would have nothing to do with the feeding, changing or bathing the baby. Jessica showed her compression marks where he had grabbed her arm and neck and he had also slapped her.
Miss Whyley advise Jessica to leave him. But she said she loved Vallance and did not want to hurt him.
Sometimes, Vallance would be out for an evening. He said he had been friends and often returned home drunk. He also got drunk when he went out with a group of Jessica's friends to a Redditch club. At one stage he accused Jessica of being with another man.
Just before Christmas 2012, he smashed up the flat, knocking a painting off the wall and pushing over the Christmas tree. When he came to the witness's 18th birthday party, he drank almost a bottle of Southern comfort whisky.
In answer to Rachel Brand QC, defending, the witness said that Vallance seemed scared to handle the baby. On one occasion when he was left in charge of the baby, he called Jessica from an adjoining room and said the baby appeared to have had a fit. Isabella was rushed to hospital and died several days later.
Kim Whyley, Drew Whyley's mother and a senior staff nurse, said the baby always screamed as though she was fearful of Vallance's voice. She had also overheard him abusing Jessica, calling her a tart, slag and whore.
The trial continues