Originally Published: 13 OCT 22 00:37 ET

Updated: 13 OCT 22 12:12 ET

By Dakin Andone, Amir Vera and Alta Spells, CNN

(CNN) -- The Parkland school shooter has avoided the death penalty after a jury recommended he be sentenced to life in prison without the possibility of parole for the February 2018 massacre at Florida's Marjory Stoneman Douglas High School -- a move that stunned the families of his victims.

The jury's recommendation Thursday, coming after a monthslong trial to decide Nikolas Cruz's fate, is not an official sentence; Broward Circuit Judge Elizabeth Scherer still is expected to issue the gunman's formal sentence on November 1. Under Florida law, however, she cannot depart from the jury's recommendation of life.

Families of the gunman's victims bowed or shook their heads as the verdict forms for each of the 17 people he killed were read in court Thursday morning. The jury found the aggravating factors presented by state prosecutors did not outweigh the mitigating circumstances -- aspects of Cruz's life and upbringing his defense attorneys said warranted only a life sentence.

None of the jurors looked in the direction of the victims' families as their verdicts were read, but instead looked down or straight ahead. Cruz -- flanked by his attorneys, wearing a blue and gray sweater over a collared shirt and eyeglasses -- sat expressionless, looking down at the table in front of him.

Cruz, now 24, pleaded guilty last October to 17 counts of murder and 17 counts of attempted murder for the shooting, in which 14 students and three school staff members were killed, and 17 others were injured.

Prosecutors had asked the jury to sentence the gunman to death, arguing Cruz's decision to carry out the shooting was not only especially heinous or cruel, but premeditated and calculated and not, as the defense contended, related to any neurological or intellectual deficits.

To illustrate their point, prosecutors detailed Cruz's thorough planning for the shooting, as well as comments he made online expressing his desire to commit a mass killing.

In their case, the shooter's defense attorneys said Cruz had neurodevelopmental disorders stemming from prenatal alcohol exposure, and presented evidence and witnesses claiming his birth mother had used drugs and drank alcohol while pregnant with him. Cruz's adoptive mother was not open about this fact with medical and mental health professionals or educators, preventing him from receiving the appropriate interventions, the defense claimed.

To decide on a recommended sentence, jurors were tasked with weighing the aggravating factors and mitigating circumstances presented by the prosecution and defense during trial.

In closing arguments Tuesday, prosecutors argued Cruz's decision to commit the shooting was deliberate and carefully planned, while Cruz's defense attorneys offered evidence of a lifetime of struggles at home and in school.

"What he wanted to do, what his plan was and what he did, was to murder children at school and their caretakers," Satz said Tuesday. "The appropriate sentence for Nikolas Cruz is the death penalty," he concluded.

However, defense attorney Melisa McNeill said Cruz "is a brain damaged, broken, mentally ill person, through no fault of his own." She pointed to the defense's claim that Cruz's mother used drugs and drank alcohol while his mother was pregnant with him, saying he was "poisoned" in her womb.

"And in a civilized humane society, do we kill brain damaged, mentally ill, broken people?" McNeill asked Tuesday. "Do we? I hope not."