A Crown attorney told the jury in a first-degree murder trial he will prove that two young men were motivated by robbery when they shot and killed Jordan Manners nearly three years ago.

The 15-year-old student at C.W. Jefferys Collegiate Institute was found on May 23, 2007, slumped in a second-floor stairwell with a gunshot wound that pierced his heart and lung.

Crown attorney Aaron Del Rizzo called the case "disturbing" and "tragic," saying that Manners knew his accused killers.

Del Risso said witnesses from the school will testify that they saw Manners in the company of his alleged killers, who are now 20 years old, before the incident and that the three were acting normally.

One witness is expected to say she saw one accused point something at Manners' chest before the victim slumped to the ground, but she did not hear a gunshot.

However, she is expected to say that one of the accused rifled through Manners' pockets before fleeing the scene.

The defendants cannot be named due to provisions in the Youth Criminal Justice Act.

Donald McLeod, who represents the defendant known as J.W. said his client was "nervous" and "scared."

"He's facing very serious charges, so where he sits is probably the most nerve-wracking seat of all," MacLeod said.

A Toronto Police forensic officer will was to be the first witness, to describe the crime scene to the jury.

Loreen Small, Jordan's mother, was one of those watching the trial. She didn't speak to reporters on the way into court.

The trial is expected to last about two months and will include testimony from as many as 40 witnesses. The jury is also expected to visit the scene of the crime at C.W. Jefferys Collegiate Institute.

Manners had just turned 15 when he was shot. He remains the only student to have been murdered by gunfire inside a Toronto school.

A memorial plaque hangs in the school to honour his memory, and a tree was also planted on the school's grounds.

His killing triggered a massive review of school safety in Toronto led by lawyer Julian Falconer.

That report didn't recommend the use of uniformed police officers in schools, but that program began in 2008.

With a report from CTV Toronto's Chris Eby