Posted October 23, 2017 14:10:30

An 18-year-old Perth man has pleaded guilty to killing his stepfather in a knife attack that started when the victim was "throttling" the teenager's seven-year-old sister, the WA Supreme Court has been told.

The teenager cannot be identified because he was only 17 when he inflicted 25 stab wounds on his stepfather at their northern suburbs home in September last year.

He was originally charged with murder and was due to stand trial next year, but today prosecutors accepted his guilty plea to the lesser charge of manslaughter.

The court was told that when the teenager started using the knife, his 36-year-old stepfather was "throttling" his seven-year-old sister.

The man then turned his attention to the youth, who continued to stab him.

Prosecutor Bernard Standish said the attack "started off being defence of another and then turned to self-defence", but because of the continued use of the knife, the teenager's response "became excessive".

Mr Standish also said there was "history" between those involved and there had been a previous confrontation between the teenager and the victim.

The 18-year-old was released on bail until he faces a sentencing hearing in February.

Justice Stephen Hall ordered that any reports prepared for the hearing examine the background of the relationship between the teenager and his stepfather.

Topics: murder-and-manslaughter, crime, law-crime-and-justice, perth-6000