(WLAX/WEUX) – The sentencing trial for the man charged in the parkland high school shooting began yesterday. The 23-year-old pleaded guilty to 17 counts of first-degree murder for killing 14 students and three teachers.

After nearly three months of jury selection, the prosecution delivered its opening statement on Monday in the trial, which will determine if Nikolas Cruz will be sentenced to death or life in prison without parole, and a teacher from Parkland High School took the stand first.

“I called 911 just out of instinct. They couldn’t hear me over the sound of the gun shots. It was so incredibly loud.”

Back in November, Cruz pleaded guilty in the mass shooting at the school on valentine’s day four and a half years ago. In the courtroom this morning, the victims’ family members held their heads and wiped away tears as lead prosecutor Michael Satz methodically recounted Cruz’s every move on the day of the massacre.

“He kneels down, he takes off his backpack, unzips his backpack and pulls out a black tactical vest. There were ten firearm magazines in that black tactical vest.”

Prosecutors claim that while evidence shows Cruz may suffer from behavioral disorders, he was not mentally unfit when he carried out the murders. Cruz’s defense team has asked to deliver its opening statements at a later date.

When the jury eventually gets the case, jurors will decide 17 times whether it should be death or life. That’s for each of the victims.