The jury in the Noah Donohoe inquest has heard the call his mother made to emergency services to report his disappearance.
During the call Fiona Donohoe expressed concerns about her son's safety.
She told the call handler it was not like her son to be out so late.
She also said she had been concerned "about his mental health".
At one point Ms Donohoe left the courtroom as the call was played to the jury.
During the 26-minute call she said she had found Noah crying in his room and she had felt he had been "overthinking" things in the preceding days.
She said she put it down to hormones and isolation.
She described him as "a deep wee thinker" who had become "very philosophical" about his life.
Earlier, Peter Coll, counsel to the coroner, told the jury that Noah had left his home on his bicycle around 5.40pm on 21 June 2020.
He took a backpack containing his laptop and a book '12 Rules for Life' by a Jordan Peterson who the court was told Noah was "quite taken with" at that time.
Noah's mother told the caller handler she had ordered it for him and that he had been "obsessed" with the book and had not left it out of his hand.
Mr Coll said CCTV had picked Noah up as he left his home and again as he cycled through the city centre.
At one point he was seen to have been without his backpack and to have discarded his clothing.
He was last seen cycling at Northwood Road and had not been wearing any clothes.
He got off his bike and went down the side of a house that led to a linear park where a stream ran into an underground culvert.
The court heard a child of Noah's build would have been able to slip through the bars on the entrance.
He was found dead hundreds of metres into the culvert six days later.
A post-mortem examination found that the cause of death was drowning.
Noah was 14 when he was found dead in a storm drain in north Belfast in 2020.
Ms Donohoe, who has led a high-profile campaign for answers, has been in court for every sitting this week.
She was accompanied by family members to watch the jury ballot.
Presiding coroner Mr Justice Rooney gave an outline of the case to the jurors, and said while they may have heard details of the case previously, it is "absolutely imperative" they remain neutral and not have a predetermined view of what happened.
He said it would be a "distressing day" for Ms Donohoe.
"She's been waiting quite some time for this particular inquest, so it will be a distressing day for her," he said.
'I miss every detail of my beautiful darling Noah'
Later the jury was played the video statement of Fiona Donohoe. It was recorded earlier this month and lasts 90 minutes.
In a highly emotional contribution Fiona Donohoe painted a picture of their lives together as a single parent family.
She described a boy who was an all-rounder, good at sport, music, he was academic and empathetic.
"We were a team in every aspect of our lives together."
She said they had joked about him becoming a doctor and building an annex at his home where his mother would live and help care for the children.
She said she believed he would have made it happen.
Since his death she said she missed the simple interactions between them. "I miss every detail of my beautiful darling Noah," she said.
It has since emerged that the night before he disappeared, Noah Donohoe left his home in the early hours.
He returned 40 mins later barefoot and without his headphones.
Fiona Donohoe said a friend had called to the house around 9pm that night. They had shared a couple of glasses of wine until around 11pm when the friend left.
She said she had gone to bed shortly after.
Noah had not emerged from his room during that visit.
She said she was aware he kept his devices in the room and would have been in contact with his friends.
"The news that he had been out that night took me completely by surprise," she said.
'Blind eye' turned to evidence
Ms Donohoe said it had been suggested that drugs may have influenced her son's behaviour on the day he went missing.
She said she knew her son well and he had shown no interest in drugs
"Nothing I’ve heard since has changed my mind," she said. She said he was a person who followed rules.
"I have no explanation for this behaviour," she said, adding that she desperately needed answers.
She said she had serious misgivings about the PSNI investigation.
And she told the court she believed that "a blind eye" had been turned to evidence that conflicted with a police theory that he’d sustained a concussion after falling from his bike.
In a supplementary statement Ms Donohoe said she and her son had used Instagram to keep in contact.
She said on occasions pre-Covid she had stayed overnight with a former partner.
She said she would not have left Noah unless sure he was safe, contactable and comfortable with the arrangement.
The inquest has concluded for the day and will sit again on Monday.
