An 18-year-old Australian girl was killed by a man she agreed to see after a Facebook meeting. Her murderer was sentenced to spend at least 21 years in jail.

Christopher Dannevig pleaded guilty to the May 2010 killing of 18-year-old Nona Belomesoff, whom she befriended online using a false identity.

Dannevig, who received his jail sentence Friday, was 20 years old at the time of the murder.

"The offender pursued a strategy involving deception and lies in order to engage and meet with the deceased and lure her to the area in which the offence occurred," Justice Peter Hall said in sentencing.

Belomesoff had made known on Facebook that she loved animals. Dannevig then made her believe he worked for a wildlife rescue group. As he convinced her he could help her find a job, they met several times before the murder took place.

Dannevig had eventually lured the young woman to the Smith Creek Reserve in Sydney for "an overnight training camp."

Belomesoff's family called the police when she did not come home the next day.

Justice Hall said the arguments and evidence presented convinced him that Dannevig killed Belomesoff, perhaps by drowning.

"The offender's actions in bringing about the death of a completely vulnerable and defenceless young woman in this way involved brutality of a high order that makes this offence a most heinous crime," Hall said.

Dannevig was sentenced to a minimum of 21 years in jail, after which he could be granted parole or get the maximum sentence of 27 years.