MEDICINE HAT, Alberta (Reuters) -
A teenage girl who is the youngest Canadian to be convicted of a multiple murder will serve the maximum sentence for killing her mother, father and younger brother, a judge said on Thursday.

The girl will serve four years in custody and another 4-1/2 years under community supervision for the Medicine Hat murders, which shocked the country because of their brutality and the fact the girl was then only 12 years old.

Her boyfriend at the time, a man 11 years her senior, has also been charged with three counts of first-degree murder but has yet to face trial.

Including time served, the girl, now 14, will serve 10 years, the most allowed against a juvenile for the crimes. She cannot be named under young-offender laws.

"Circumstances surrounding these murders are horrific," Alberta Justice Scott Brooker said.

"It is difficult to imagine or conceive of a more horrific crime than this, the planned and deliberate murder of her parents and only sibling by a 12-1/2-year-old young person."

A jury in July found the girl guilty of first-degree murder following a month-long trial, during which gruesome details of the attack came to light.

The bodies of her father, 42, mother, 48, and brother, 8, were found in the family home in April 2006, stabbed 41 times.

The judge, the defense and the prosecution all agreed the girl's boyfriend, Jeremy Steinke, who had claimed to friends he was a werewolf, killed them in an early-morning attack.

But prosecutors convinced the jury that the girl helped plot the crime in revenge for being grounded and having her computer privileges revoked.

She stabbed her brother a few times during the attack, had sex with Steinke after, then fled with him to neighboring Saskatchewan. The pair were arrested there.

The defense tried to show that the girl "vented" to friends about wanting her parents dead for forbidding her any contact with Steinke, but never believed the killings would be carried out.

"You can never undo what you did to your mom, dad and brother," Brooker said, looking at the girl following his sentencing decision. "However, what you can do is honor their memory by dedicating your life to becoming the woman your parents and brother would be proud of."

The girl's lawyer said she is holding up well considering her circumstances and is looking forward to treatment.

Steinke also appeared Thursday in court, where a judge granted his request for a hearing in February to seek a change of venue on the grounds that an unbiased jury would be too difficult to assemble due to publicity over the case in the small southeastern Alberta city.

Holy cow man, just what is this world coming to? 12! Wow. And I just revoked my daughter's computer privileges and she's 12!
Good thing I didn't ground her!
It's a good thing she doesn't have a 23 year boyfriend. Sick bastard. Should be hung by his balls as well as tried for murder.