A Toronto judge has declared a mistrial in the case of two men charged with the high-school murder of 15-year-old Jordan Manners, after the jury failed to reach a verdict.

The jurors had been deliberating for four days when Justice Ian Nordheimer declared the mistrial shortly after 5 p.m. on Friday.

Two 20-year-old men accused in the case pleaded not guilty to first-degree murder in Manners' shooting death. They cannot be identified because they were minors when the murder occurred, and are known only as J.W. and C.D.

Manners' body was discovered in a stairwell at C.W. Jefferys Collegiate in Toronto on May 23, 2007. The Grade 9 student was shot in the heart. He was the first person in Toronto to die in a school shooting.

Crown lawyers argued the two defendants planned the killing. One shot Manners while the other rifled through his pockets, they alleged.

The jury also heard that Manners had a chain stolen from around his neck.

Lawyers of the accused said the Crown had failed to prove its case beyond a reasonable doubt. There was a lack of evidence, such as fingerprints and gunshot residue, they argued.

Lydia Riva, the lawyer who represented C.D., said she thought the jury had reasonable doubt.

"We know they took their time and they tried their best, and this sort of thing happens," Riva told reporters outside the courthouse. "It's a very serious matter and they took it seriously. Unfortunately, we don't have an answer."

Lawyer Donald McLeod, who represented J.W., said his client is an innocent man who had been hoping to go home but will now remain in jail.

He added that he hopes both accused men will be able to get a fair trial, in spite of the media attention the case has received.

On Thursday, the jury told the judge they were at an impasse, but resumed deliberations nonetheless Friday morning on orders from the judge. They had been trying to reach a verdict since Tuesday afternoon.

At trial, two teenage girls who were central witnesses in the case backed away from statements they had made to police.

One of them told the court she couldn't remember what happened. The other said she had based her recollection on gossip. Earlier she had told police that Manners was dragged down the stairs "like a rag doll."

Crown attorney Tom Lissaman told the court that fear "had taken these young girls hostage and made them deny" what they had witnessed.

Justice Nordheimer told the court that the two teenaged witnesses had "undermined the process," and asked Ontario's province's attorney general to look into the matter.

The ministry said it would not comment until a verdict is reached in the case.

Manners' death prompted major school-safety reviews in the city. It also prompted uniformed officers to begin patrolling some Toronto schools.

With files from The Canadian Press