Connor Gibson, 20, was convicted of attacking Amber Gibson in woodland in Hamilton, South Lanarkshire, in November 2021.

He removed her clothing, sexually assaulted her with the intention of raping her, inflicted blunt-force trauma to her head and body, and strangled her.

Gibson denied the charges but was found guilty after a 13-day trial at the High Court in Glasgow.

Following the verdicts, Judge Lord Mulholland told Gibson: "Your sister - the last person she saw was you strangling her. It was depraved and you will pay a heavy price for that."

An unrelated man who intimately touched Amber's body and left his DNA all over her after finding her dead - but didn't contact police - was also found guilty.

Amber was reported missing on the evening of Friday 26 November and her body was discovered in Cadzow Glen on the morning of 28 November.

Gibson was arrested three days later.

The day before he was detained, he posted a chilling tribute to the sister he murdered, writing on Facebook: "Amber, you will fly high for the rest of time.

"We will all miss you. Especially me. I love you ginger midget. GBFN (goodbye for now) X."

A post-mortem of Amber's body found she was covered in mud and the cause of death was "compression of the neck".

Jurors also heard other evidence that "widespread blood staining" on Gibson's jacket was compatible with Amber and his DNA was also found on her shorts, worn as underwear, which had been "forcibly torn" off.

The court heard Gibson, also known by the surname Niven, did not seem emotional as he spoke to his and Amber's former foster father, Craig Niven, on the day her body was found.

Giving evidence, Mr Niven had said he would not leave the siblings in each other's company because they were "not a good mix".

Mr Niven and his wife had fostered the siblings since Amber was three and her brother was five. The couple were granted permanent care of the siblings a few years later.

At the time of Amber's murder, Connor was living at the Blue Triangle homeless hostel in Hamilton while Amber was at the town's Hillhouse children's home.

Mr Niven told the court he had not heard from his former foster son during Amber's disappearance but, in a call on the day her body was discovered, Gibson told him the pair had "fallen out" when they saw each other two days previously.

Jurors also heard from Peter Benson, of Police Scotland's cyber crime group, who examined a phone found where Gibson was living.

It showed that on 27 November at about 12.34am, the phone's user wrote to a Snapchat group with five recipients: "I'm really going to need you guys help with something when yous come back. I'm being serious."

Around 40 seconds later the user messaged Amber on the app: "Are you ok?"

The user then told the group chat at approximately 1.33am: "nvm (never mind) it's all good."

The search history obtained from the phone also showed the user searched "how to get nosy police officers to stop monitoring your phone" at 11.38pm.

Read more from the trial:
Amber Gibson 'had injuries consistent with being strangled'
Blood on brother Connor Gibson's clothes 'could indicate assault'

Iain Currie, manager of Hillhouse children's home, told the court he spoke to Gibson at about 9pm on 26 November after he called to speak with his sister, but noted him appearing "sharp" on the phone after making no greeting.

Also on trial was Stephen Corrigan, 45, who was found guilty of attempting to defeat the ends of justice by intimately touching and concealing Amber's body after discovering her at some point in the following two days, instead of contacting the emergency services.

Corrigan, who the court heard was not known to Gibson, also denied the charge and had lodged a special defence of alibi.

His father, William Corrigan, 79, told the court his son was at his home in Blantyre, South Lanarkshire, that weekend after a fall on ice left his arm in a sling, and denied lying to protect him.

The court heard Corrigan told police he was at a "complete loss" to explain why his DNA was found on 39 areas of Amber's body, including her breasts, buttocks and thighs.

Judge Mulholland told Corrigan he faces a "lengthy sentence".

The judge deferred sentence until 4 September at Livingston High Court for pleas in mitigation and background reports.

Following the verdict, foster parents Craig and Carol Niven said in a statement: "When they arrived at our home, Amber was three and Connor aged five.

"Connor stated 'we are safe'. They were until he took the safety away. Amber deserved to live a life of hope and opportunities. As a family, we will never be able to get over how this was taken from her.

"We are relieved the people involved in what happened to her are now behind bars. However, no amount of time will be justice enough for such a young innocent life."

They described Amber as the "most giving, caring, loving, supportive and admirable person" who had a love of art and singing.

The couple added: "She had the most amazing outlook on life considering the suffering she had experienced."

They also commented how they had listened to evidence "how much Amber and Connor have been let down throughout their lives by the system".

The statement added: "As a family, we all feel this could have been prevented. We now have one daughter buried in Larkhall Cemetery and another child in prison. We really miss Amber - life will never be the same."