Prosecutors in the case of Florida school shooter Nikolas Cruz are calling for an investigation after a juror said she felt threatened by another member of the jury during deliberations that ended Thursday with a life sentence for Cruz's murder of 17 people.

The motion calls for law enforcement to interview the unnamed juror after she told the state attorney's office "she perceived to be a threat from a fellow juror while in the jury room." No further details were given. A hearing is set for Friday afternoon.

A divided jury spared Cruz the death penalty and instead decided to send him to prison for the rest of his life in a decision that left many families of the victims angered, baffled and in tears. Cruz, 24, pleaded guilty a year ago to murdering 14 students and three staff members, and wounding 17 others, at Parkland's Marjory Stoneman Douglas High School on Feb. 14, 2018.

Under Florida law, a death sentence requires a unanimous vote on at least one count. The seven-man, five-woman jury unanimously agreed there were aggravating factors to warrant a possible death sentence, such as agreeing that the murders were "especially heinous, atrocious, or cruel."

But one or more jurors also found mitigating factors, such as untreated childhood issues. In the end, the jury could not agree that the aggravating factors outweighed the mitigating ones, so Cruz will get life without parole. Circuit Judge Elizabeth Scherer will formally issue the life sentences Nov. 1. Relatives, along with the students and teachers Cruz wounded, will be given the opportunity to speak.

The jurors pledged during the selection process that they could vote for a death sentence, but some victims' parents, some of whom attended the trial almost daily, wondered whether all of them were being honest.

Juror Denise Cunha sent a short handwritten note to the judge Thursday defending her vote for a life sentence and denying she intended to vote that way before the trial began.

"The deliberations were very tense and some jurors became extremely unhappy once I mentioned that I would vote for life," Cunha wrote. She did not explain her vote and it is unknown if she is the juror who complained to the state attorney's office.

Jury foreman Benjamin Thomas told local reporters that three jurors voted for life on the final ballot. Two were willing to reconsider, but one was a "hard no" for the death penalty.

"It really came down to a specific (juror) that he (Cruz) was mentally ill," Thomas said. He did not say whether that person was Cunha.

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Izaguirre reported from Tallahassee, Florida.

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