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

Two teenage sisters in Ontario have been found guilty of first-degree murder in the bathtub drowning death of their mother, a judge ruled on Thursday.

"The two defendants set out to commit the perfect crime, but instead they created the perfect prosecution," said Justice Bruce Duncan, who heard the case without a jury.

"The case against them is overwhelming. It is probably the strongest case I have ever seen in over 30 years of prosecuting, defending and judging criminal cases."

Prosecutors say the teens, who were 15 and 16 at the time of the crime, plied their mother with drugs and alcohol on Jan. 18, 2003, before one of them held the victim's head underwater until she drowned.

The defence argued that the mother was an alcoholic who was in a self-induced stupor when she accidentally drowned in the tub.

However, the court heard that the defendants described to a family friend how they had killed the 44-year-old victim and planned to make it look like an accident. When the friend contacted police, the investigation was reopened into what had been classified as an accidental death.

During the trial, the court saw a videotape in which the defendants separately admitted to the murder.

Defence lawyers argued the girls falsely claimed to have killed their mother because they craved attention.

The two women, now aged 18 and 19, had pleaded not guilty to the charges. Neither showed any emotion as the verdict was read.

The pair, who had been under house arrest since their arrests, were taken into custody after the verdict was delivered.

Because of their ages at the time of the death, neither they nor their mother can be identified under the terms of the Youth Criminal Justice Act.

They are expected to be sentenced in the next two or three months.

If sentenced as adults, the two could face life in prison with no chance of parole for a minimum seven years and their identities could be revealed.

Should they be sentenced as youths, they could face a maximum of 10 years with no parole for six years and their identities would remain protected.