Two 14-year-old boys have pleaded not guilty to murdering Anastasia Kriegel in Dublin last year.
One of the boys also pleaded not guilty to the aggravated sexual assault of the 14-year-old, whose body was found at a derelict farmhouse in Lucan, Co Dublin, almost a year ago.
The boys cannot be identified because of their age.
The jury has been selected for the trial which is expected to last up to six weeks.
Both boys sat beside their guardians at the Central Criminal Court on Monday where they were accused of murdering the schoolgirl at Glenwood House in Lucan on May 14 last year.
Anastasia’s naked body was discovered at the derelict house three days later.
Both boys were 13 at the time.
Mr Justice Paul McDermott told the jurors to ensure they are not connected to the case.
“If you have a connection with those events you should not serve on this jury,” he added.
He said the case was covered by the media during the investigation, adding: “If there is any element you feel may prevent you from an independent assessment and judgment arising from any knowledge you may have, you should bring that to my attention.”
He warned that the case involves the allegation of murder and aggravated sexual assault and added: “They involve young people so that may make it more upsetting than other cases of this kind. These are serious offences.”
More than 130 witnesses including gardai, forensic experts and doctors are due to give evidence.
Justice McDermott reminded the jury that the accused are entitled to have their identities protected and it is an offence for anyone to broadcast or publish their details.
He also warned the jurors not to disclose any details of the case they have heard.
He added that any publication of the boys’ identities would be contempt of court.
A jury of eight men and four women were sworn in to hear the trial. The opening statements are expected to be heard on Tuesday.