A 16-year-old who took his own life in Polmont Young Offenders Institution had been removed from suicide watch hours earlier, a fatal accident inquiry heard.

William Brown, also known as William Lindsay, was remanded in custody after being deemed a “potential risk to public safety” at Glasgow Sheriff Court on October 4 2018, three days before his death, the inquiry heard.

The joint inquiry at Falkirk Sheriff Court is investigating his death and that of Katie Allan, 21, after both were found dead in their cells in separate incidents at Polmont in 2018.

On October 3, Mr Brown had walked into a police station with a knife, while on bail for another blade offence, the inquiry heard in a statement of agreed evidence.

Despite a plea to bail him due to a lack of beds in a secure unit, Mr Brown was remanded to Polmont, where he died in custody.

Before he was taken there, Mr Brown was asked by a social worker if he was suicidal, and replied: “No, not now, but I don’t know how I’ll be in prison.”

Since 2016, Mr Brown had been taken to hospital due to suicide attempts and ideation, excess drug use and fighting on 15 occasions in two years, and was initially put on a 30-minute observation at Polmont when he arrived, “for reassurance and safety”.

On October 5, a case conference was held with a mental health nurse and two prison officers, where Mr Brown was assessed as “at no apparent risk of suicide” and was removed from 30-minute observations – but less than two hours later was referred to the mental health team by a social worker.

Mr Brown was found dead in his cell at 7.40am on October 7 – nearly 12 hours after last having contact with Scottish Prison Service (SPS) staff at 8.55pm.

His brother, John Reilly, felt “Polmont could not afford to keep William alive”, the solicitor representing both families, Aamer Anwar, told a press conference outside Falkirk Sheriff Court.

Both Mr Brown and Ms Allan had been assessed with the Talk To Me scheme.

In a statement outside court, Mr Anwar said both families want Humza Yousaf to work to remove Crown immunity, which means the SPS is exempt from prosecution for the deaths; set up an independent body to investigate prison deaths; and impose a year’s limit for the start of an FAI.

The loss of any person in our care is devastating and we recognise the profound impact it has. Everyone who enters custody is assessed to identify what support is needed

He said they also want the First Minister to hold SPS to account and ensure families get automatic legal representation at an FAI.

The inquiry heard Ms Allan, who died aged 21 on June 4 2018, was found to have traces of an antidepressant which was not prescribed to her, during a post-mortem examination.

At a family visit on June 3, her mother, Linda Allan, had told prison officers the Glasgow University student was being “berated” by other prisoners and was “terrified”.

Ms Allan, who suffered from alopecia, had a history of self-harming which prison staff were aware of.

She was last seen alive by a prison officer as she watched TV, and said “Hi”, just after 8pm, before taking her own life. She was found by a prison officer just before 6am on June 4.

Ms Allan had lost seven kilos (15lb) while in custody over a period of four months after being jailed for a drink-driving offence.

In April 2018, her solicitor had urged the Scottish Prison Service to get her medical treatment for alopecia and eczema.

Ms Allan had been given a hair piece and her next appointment with a doctor was more than a month after her death, on July 6 2018.

She had abandoned an appeal against her 16-month sentence on May 29.

A toxicology report during a post-mortem examination found 0.034mg per litre of mirtazapine – an antidepressant, which Ms Allan was not prescribed.

Ms Allan’s parents, Linda and Stuart, stood with Mr Anwar as he made a statement on their behalf, saying they “believe that the SPS have no accountability for the avoidable deaths of young people”, saying that while the Crown Office found “evidence to pursue a criminal prosecution against the Scottish Prison Service but Crown immunity prevents them from doing so”.

Deborah Coles, executive director of Inquest, backed their call to lift Crown immunity, adding: “The deaths of Katie and William really should shame us all.”

A SPS spokesperson said: “The loss of any person in our care is devastating and we recognise the profound impact it has. Everyone who enters custody is assessed to identify what support is needed.”

They said it would be inappropriate to comment further given the FAI.

A spokesperson for the Crown Office said: “We acknowledge that the wait for these proceedings has been too long and has caused distress for Katie and William’s families.

“The FAI will allow a public airing of all the evidence at which families and interested parties will be represented.

“The families and legal representatives will continue to be kept updated as the inquiry progresses.”

A Scottish Government spokesperson said: “Our thoughts are with every family who has been bereaved by suicide in prisons.

“Fatal Accident Inquiries are a matter for the independent Crown Office and Procurator Fiscal Service.

“We cannot comment on these cases with the approaching Fatal Accident Inquiry and we will carefully consider the outcome.”