Two 17-year-old teenagers will begin to be tried this Monday by a juvenile court in San Isidro, accused of the crime of businessman Andrés Blaquier, murdered by a shot to the chest on October 29 of last year when they tried to steal his motorcycle while he was riding. along the Pan-American highway, in the Buenos Aires district of Pilar, judicial sources reported.   The debate will be led by the Juvenile Criminal Responsibility Court 1 of the Judicial Department of San Isidro and will begin at 10 in the courts located on 12 de Octubre Avenue 1475, west collector towards the capital, in the north of the Buenos Aires suburbs.   Both teenagers are charged with "robbery aggravated by the use of a firearm and resulting in serious injuries, in real competition with homicide tripled aggravated by being 'criminis causa', by treachery and by having been committed with a firearm" to the detriment of the murdered Andrés Blaquier (62), and his partner Magdalena De Elordy, who suffered a fracture of the kneecap of her left knee during the incident.   Because the trial will involve two minors as defendants, the spokespersons clarified that it will be a trial reserved for the parties.   Also for this reason, the sources indicated that in this first instance it will only be decided whether the accused are innocent or guilty, so no possible penalties will be imposed.   In this regard, if the guilt of the accused is proven, a caesura trial will be held to determine the corresponding penalty.   The magistrates in charge of the process will be Alejandro Flori, Silvia Chomiez, Patricia Klentak, while the prosecutor Paula Romeo will represent the Public Ministry