Judge addresses Mississauga teenagers found guilty of drugging and drowning their mother. ((CBC))

Two sisters in Mississauga, Ont., who wereconvicted of killing their mother in a bathtub in 2003 have been sentenced as youths, and given the maximum penalty.

Justice Bruce Duncan sentenced both to 10 years in prison.

The two, now 19 and 20 years old, will serve six years in secure custody and four years under conditional supervision, with 18 months subtracted for time spent in prison.

The older sister will serve her sentence in an adult facility.

The decision was announced late Friday afternoon at a court in Brampton, Ont. Their names can't be released because they were 15 and 16 at the time of the crime, and subject to terms of the Youth Criminal Justice Act.

In convicting the sisters last December of first-degree murder, thejudge found the girls plied their mother with Tylenol-3 pills and alcohol on Jan. 18, 2003, before one girl held the mother's head underwater until she drowned.

A psychiatric assessment released Thursday recommended the girls be sentenced as youths, citing concerns that the two would do poorly in an adult prison.

Dr. Phil Klassen told a sentencing hearing that the sisters had no history of violence or criminal behaviour before killing their mother.

Initially, the death of the 44-year-old mother was ruled accidental, but police reopened the case a year later when a friend of the sister contacted them with new information.