The stunned couple who took in Nikolas Cruz after the death of his mother has spoken for the first time about the troubled teenager suspected of killing 17 students and staff at his former high school in Florida on Valentine's Day.

Kimberly and James Snead described the 19 year-old as immature, quirky and depressed - but pleasant and growing happier and giving no clues of the horror he was about inflict as he plotted the massacre under their roof.

“We had this monster living under our roof and we didn’t know,” Kimberly Snead told the South Florida Sun Sentinel. “We didn’t see this side of him.”

“Everything everybody seems to know, we didn’t know,” James Snead said. “It’s as simple as that.”