The mother of a nine-year-old boy murdered by his father has wept in court, as the man admitted to beating their son for a period of months in the lead-up to his death.

Graham Stuart Dillon, 39, pleaded guilty to his son Bradyn's killing, along with causing grievous bodily harm and several assault charges including choking and threatening to kill.

Documents tendered to the court revealed for the first time the extended period of abuse Dillon inflicted on his son in the months before his death in February 2016.

They detailed more than 60 separate injuries to Bradyn's head and body, and chronicled incidents where Dillon stubbed out cigarettes on his son's skin, threw him against a wall, and punched him in the stomach.

They also revealed an ambulance was not called for the boy for more than seven hours after he was beaten unconscious.

He later died in hospital of brain injuries.

Bradyn's mother Rachel Jones and other family members wept in the back of the court as Dillon pleaded guilty to all charges.

Dillon was expected to face trial in October.

Final beating sparked over 'stolen lollies'

Nine-year-old Bradyn Dillon died in February 2016. ( Supplied )

Court documents reveal Bradyn was hit in the head multiple times between December 2015 and February 2016.

The final beating, which caused previous brain injuries to re-bleed, was sparked over an accusation Bradyn had stolen lollies from his father.

Dillon had just beaten Bradyn with a belt as he was bent over naked on a coffee table.

"Bradyn told the accused he didn't want to live with him anymore and that the belt did not hurt," the documents said.

Dillon then forcefully hit and kicked his son in the face and head.

When Bradyn fell unconscious, his father made numerous internet searches under titles including "knocked out myths and facts about concussions," and "how to wake somone [sic] who passed out".

No ambulance was called for Bradyn for seven-and-a-half hours after he fell unconscious.

"The assault caused fresh brain injuries and also caused the older brain injuries to re-bleed," the documents said

Bradyn Dillon had been beaten for months leading up to his death. ( Supplied )

"The aggregated brain injuries caused Bradyn's death on the evening of February 15, 2016."

Documents reveal extent of abuse

The documents tendered in court outline a terrifying escalation of violence by Dillon, particularly towards the time of the murder.

"The violence was often punishment for a real or imagined infraction of discipline," the documents said.

"The offender sometimes used his own body to inflict serious injuries.

"At other times he used items such as lit cigarettes and metal boxes."

Other injuries inflicted on Bradyn also included a broken rib, after his father punched him in the stomach with a closed fist.

On another occasion a witness saw Bradyn with a black eye, but Dillon told the man his son had fallen off his bike.

The court documents detail other incidents where Bradyn was thrown against a wall, and suffered burns when his father stubbed out a cigarette on his skin.

Death raised questions over child protection

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The death sparked an urgent ACT Government review of child protection services in Canberra.

Bradyn's mother slammed the ACT Government over failures in the system.

"I spoke with the police, with child ... protection. Every card that was offered to me, I rang them on a daily basis, on a weekly basis. I was going into the police station," Bradyn's mother Ms Jones told an ABC documentary in 2016.

"I was ridiculed, I was mocked. They made me feel like I had problems or I was trying to make problems."

Dillon will be sentenced in December.