A Mississauga man who helped two teenage sisters plan their mother's murder has been sentenced to one year in jail.

Madame Justice Francine Van Melle also ordered the 19-year-old to an additional six months of conditional supervision, the Toronto Star reports.

The man, who cannot be named because was 15 years old at the time of the crime, did not say anything when given the chance to speak at the Brampton courthouse on Monday.

A jury convicted him of conspiracy to commit murder in December in connection with the 2003 murder of an alcoholic mother by her two daughters.

The sensational trial for the siblings, dubbed the "bathtub murder sisters," ended with two first-degree murder convictions. The pair, now 20 and 19 years old, was sentenced as youths in June to the maximum 10 years.

The identities of the young women and their alcoholic mother who they drugged and drowned in their home also cannot be published under the Youth Criminal Justice Act (YCJA).

At trial, court heard the 19-year-old man helped the sisters plan the murder and he supplied them with the Tylonel-3 pills used to stupefy their mother before drowning her.

The Crown used disturbing electronic messages between the young man and the younger sister as evidence of the man's role in the killing.

In the computer chats, the pair discussed what to do if the mother suddenly woke up while the girls were drowning her. The man also offered advice on how the sisters should act while talking to police after calling 911 to report the death.

"Although I find that (the young man) was not a leader in the offence, the fact is that he contributed to the offence," Justice Van Melle said Monday, according to the Star.

Crown prosecutor Mike Cantlon had sought the maximum three-year term for youths sentenced under the YJCA, while defence lawyer Alison MacKay asked for psychiatric counselling or mandatory supervision in lieu of jail time.

The man could have faced a life prison sentence if he had been sentenced as an adult.

Van Melle said the man, who has no prior criminal record, showed a lack of remorse.

"He shows little insight into the harm to which he contributed, and the fact that his actions assisted in a murder," she said.

"He is by all accounts a very intelligent young man and as such should have been aware of the harm his actions could bring about."