The Parkland school shooter faces the death penalty as his trial begins

The sentencing trial for the gunman who killed 17 people at Marjory Stoneman Douglas High School in Parkland, Fla., more than four years ago is set to begin on Monday.

After nearly three months of jury selection, jurors must decide whether Nikolas Cruz, 23, gets a life sentence in prison or is put to death. He has already pleaded guilty to all charges.

Prosecutors are seeking the death sentence, while Cruz's defense team is hoping for the only other option: life in prison with no possibility of parole. (In Florida, life sentences don't allow for parole.)

A jury of seven men and five women will hear witness testimony and review evidence, during a trial that's expected to last for months.

The jury must be unanimous in deciding to impose the death penalty. If a single juror disagrees, Cruz will be sentenced to life.