A Sydney court has heard former nurse Roger Dean should be jailed for life for murdering 11 residents in a nursing home fire.

Summing up at Dean's sentencing hearing, crown prosecutor Mark Tedeschi, QC, said that at the time of the murders, Dean, 37, had the capacity to make "sophisticated and complex decisions".

Mr Tedeschi said Dean posed a risk to the community because he had a history of narcissism and would continue to put his own needs above the rights of others.

"The level of culpability in the commission of this offence is so extreme that community interests in retribution, punishment, community protection and deterrence can only be made through the imposition of a life sentence," Mr Tedeschi told the Supreme Court.

Mr Tedeschi said Dean knew people would die when he set the Quakers Hill nursing home on fire in November 2011.

The former registered nurse has pleaded guilty to 11 counts of murder and eight of recklessly causing grievous bodily harm after lighting two fires to try to hide his theft of prescription drugs.

One fire was in a bedroom where two elderly residents were asleep.

Some residents died in the fire and others afterwards from their injuries.

Mr Tedeschi told the court that that before he lit the fires, Dean was one subject away from qualifying for a law degree at Macquarie University.

He said Dean had achieved high distinctions and had won a university prize for ethics.

The prosecutor said Dean stole drugs from the home because he ran out of money to keep "doctor shopping" and buying the prescription drugs he was addicted to from chemists.

"He made the decision to help himself to the drugs at the home," he said.

Mr Tedeschi said Dean had also applied for a more senior nursing job at the home.

He said the former nurse was "in a better position than most" to understand he was addicted to prescription drugs but chose not to get professional help.

Justice Megan Latham will sentence Dean at a later date.