The disturbing details of a deadly attack on a Perth teenager have been revealed in court as three boys admitted to killing him for just $175.

Quinn De Campe died in hospital the day after he was viciously set upon in Balga in December last year.

Family and friends of Quinn were shocked by the events that led to the 16-year-old's death.

Today, four teenage boys were due to stand trial accused of his murder.

Instead, three pleaded guilty to the lesser charge of manslaughter and aggravated armed robbery.

Absolutely senseless.