Video report by ITV News Correspondent Sejal Karia
A "deeply unpleasant" man who covered up the death of a three-year-old crushed by a car seat has admitted manslaughter.
He then organised a cover-up in a bid to avoid being implicated in the little boy's death.
At his first trial, Waterson denied a manslaughter charge but was ordered to face a retrial after a jury failed to reach a consensus.
Ahead of the start of his second trial, Mr Waterson from Croydon pleaded guilty to manslaughter on the basis he only pushed the seat into the child once.
Alfie's mother and Waterson's girlfriend, 24-year-old Adrian Hoare from Gravesend in Kent, was previously found guilty of child cruelty and jailed for two years and nine months for her role in failing to prevent her son's death.
Both defendants had admitted conspiring to pervert the course of justice by lying to police.
Waterson was convicted of intimidating a witness and Hoare of assaulting another witness.
Alfie is the only person in the UK to have died from crush asphyxiation as a result of an electronic car seat, police said.
Scotland Yard’s Detective Chief Inspector Simon Harding branded Waterson "arrogant, selfish and deeply unpleasant" and said justice had been served for Alfie.
On February 15 last year, the defendants had gone shopping for cushions in Sutton, accompanied by Alfie, Emilie Williams, 19, Marcus Lamb, 22, and another young child.
CCTV footage shown in the original trial pictured him running to keep up with his mother for their return trip home.
The court was told how Alfie was killed after Waterson pushed his electronically-controlled seat into him as he sat in the footwell.
The seat compressed Alfie into a space of just 9.5cm, causing severe chest injuries.
But Waterson ignored his cries for help, instead saying: "I won’t be told what to do by a three-year-old."
By the time emergency services arrived, it was too late to resuscitate Alfie who had collapsed after being injured.
He died from crush asphyxia three days later.
Officers soon began to close in on Waterson, but he gave them a false name, statement and sold the car in question.
He also intimidated witnesses, threatening to make them "disappear" if they did not stick to stories which absolved him of wrongdoing.
His crime was eventually revealed after his girlfriend's half-sister recorded a conversation with her family member in which she disclosed what happened. The recording was then handed to police.
Waterson then blamed his step-brother for the death.
Jurors in the original trial failed to reach a consensus, leading to a retrial being ordered.
On hearing his guilty plea to manslaughter at the start of a second trial, Judge Mark Lucraft QC remanded Waterson into custody to be sentenced on Monday, September 9.