Kimberly Ruth Noyes is standing trial on charges of second-degree murder in the death of neighbour John Fulton, 12. (CBC)A Grand Forks, B.C., woman has pleaded not guilty to killing a 12-year-old autistic boy in August 2009.

Kimberly Ruth Noyes entered the plea Monday as her trial began on a charge of second-degree murder in connection with the death of John Fulton, who was autistic.

Crown attorney Phillip Seagram told the court in his opening statement that there was no doubt Noyes killed Fulton. The only issue in the case is Noyes' mental state at the time, said Seagram.

Court heard that Noyes has a long history of mental illness following the birth of her third child.

Noyes, 53, was charged after the boy was found dead in her townhouse last Aug. 17, two days after he had disappeared from the front steps of his home, two doors away from where he was found.

John Fulton, 12, was found dead inside a neighbour's home in Grand Forks, B.C., in August 2009. (CBC)

Fulton was stabbed through the neck with a kitchen knife, after which he would have lost consciousness within seconds, the court was told Monday.

Several witnesses, including police, doctors, and friends of Noyes are expected to testify in the case, which is being heard by a judge without a jury.

The B.C. Supreme Court trial is being held in Rossland, 50 kilometres east of Grand Forks and about 400 kilometres east of Vancouver.