Emergency services were called to a home on Australis Drive at Ropes Crossing, near Blacktown, about 2.50am on June 4, where they found the teenage boy suffering a stab wound.
Officers performed CPR until paramedics arrived, however the teenager died at the home.
Detective Chief Inspector Paul Tickner said on the day of the event he believed the alleged offender to be the boyfriend of a mutual friend, who had been invited to the party by a teenage girl at the gathering.
"Young boys, probably with some hormones running through their system, and somebody thought they had to defend the rights of their girlfriend at the scene," he said.
"Unfortunately it's led to a young boy being killed. They shouldn't have been carrying knives in the first place."
The mutual friend's boyfriend brought two other males with him, police said at the time.
Strike Force BOBR was established to investigate the incident, with detectives and members of the State Crime Command's Homicide Squad assisting the investigation.
Police launched public appeals for information and executed two search warrants on Thursday, at homes on Pages Rd, St Marys and Jill St, Marayong where they seized a number of items for forensic examination.
Two boys, both aged 17, were arrested at the homes, and a third teenager, aged 16, was arrested in Tregear a short time later.
The trio were taken to Mt Druitt Police Station where they were charged with murder, affray and wield knife in public place.
They were refused bail and will appear at a children's court on Friday.
Inquiries under Strike Force BOBR continue.
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