The Central Criminal Court has heard how 21-year-old Wayne O'Donoghue told gardaí he had grabbed schoolboy Robert Holohan by the neck but did not mean to kill him.
Mr O'Donoghue, of Ballyedmond near Midleton in Co Cork, denies murder but has admitted manslaughter.
11-year-old Robert was killed at Ballyedmond on 4 January this year. He died from asphyxia caused by manual strangulation, the jury heard.
His body was wrapped in black plastic and in garda statements Mr O'Donoghue explained how he drove to Inch Strand to dump the body, stopping along the way in Midleton to buy a lucozade.
The court, which is sitting in Cork, heard that Mr O'Donoghue said the killing was an accident and the little boy was like a brother to him.
The trial before a jury of seven women and five men is expected to last at least three weeks.
Mr O'Donoghue, an engineering student, was arrested on 17 January.
