Florida school shooting suspect Nikolas Cruz has been formally charged with 17 counts of first-degree murder over the Valentine's Day massacre.

It means he could face the death sentence if convicted.

A grand jury in Fort Lauderdale returned the indictment against the 19-year-old for February 14 mass shooting at Marjory Stoneman Douglas High School in Parkland in which 17 people died and 16 were wounded.

The indictment also charges Cruz with 17 counts of attempted murder.

Cruz's public defender said the teenager will plead guilty if prosecutors take the death penalty off the table, which would mean a life prison sentence.

The Broward County state attorney has not announced a decision on the death penalty.

Seventeen people were killed in the Valentine's Day massacre. Credit: PA

The couple who provided a home to Cruz before the massacre had earlier given evidence before the grand jury considering the case charges.

James and Kimberly Snead each spent about half an hour in closed-door evidence on Wednesday before the panel.

Their lawyer Jim Lewis says they answered all questions and were fully cooperative.

Mr Lewis says the couple were shocked by what happened and did not foresee Cruz doing something like the shooting.

The Sneads took in Cruz after he briefly lived with a family friend following the death of his mother in November.