A Sydney mother has wept as she told a jury of finding her severely disabled son dead in the bathtub after her estranged partner screamed out to her around two o'clock in the morning.
"He was in a fetal position .. curled up," Rebecca Horton testified on Tuesday in the NSW Supreme Court.
Her former partner, Charlie Younes, 45, has pleaded not guilty to murdering 18-year-old Steven Copo Horton in October 2013 at the Emerton house she had just moved into in Sydney's west.
Steven was born with severe intellectual and physical disabilities and was incapable of walking and talking, but could move himself about by crawling or shuffling along on his bottom.
Crown prosecutor Rohan Cooley alleged Younes "used a hand or hands to force, in some fashion, by applying pressure to the neck area of the deceased, force him under the water, thereby in effect drowning him".
Ms Horton said Steven, whose mental age was that of a toddler, was "happy all the time", everything made him excited and he constantly made "happy scream" noises.
She got together with Younes in 1997 but the relationship deteriorated by 2013 and he reacted angrily when she moved into the Emerton house a week before her son's death.
"He wanted me to go back to the other house," she said.
"Then he wanted to move into that house and sell his house... It wasn't going to happen."
Younes kept on turning up at the new house and had wanted to stay over the night before her son died, but she told him to leave.
"Just after two o'clock in the morning I heard Charlie screaming out my name," she said.
She jumped out of bed, saw other family members in the hallway and Younes either in the bathroom entrance or more inside the room.
Steven, who was wearing his pyjama pants, was in a fetal position in the bath.
They placed him on his bed, but "you could tell he had died".
Ms Horton said she did not think her son could have pulled out the pin on the bolt on the "half" door to his bedroom to get out into the hallway, or then to have moved quietly past his wheelchair in front of the door.
"When he is crawling around he continually makes noises," she said.
While he could have pulled himself into the bath, there would have been some noise and she did not think he would be able to turn on the taps.
Mr Cooley told the jury Younes told ambulance officers something like he had found Steven after waking up and hearing water running.
He told police at the scene he had been watching TV when he heard the water running for some time.
He said he thought Ms Horton was having a shower, but when he went to investigate, found Steven's body.
In his later police interview, Younes gave a third version saying he knocked on the front door as he didn't have a key, but couldn't alert anyone to let him in.
Younes said he thought he heard water running so he went to the back of the house where the bathroom was located, "shimmied up" through an open window and discovered Steven dead in the bath.
Ms Horton will be cross-examined by defence lawyer Leah Rowan on Wednesday.