Valentine's Day Massacre. Florida shooting – Ex-pupil kills 17 and leaves dozens injured in US school bloodbath

AN expelled student wearing a gas mask and carrying smoke grenades went on a rampage at his former school killing at least 17 people and injuring dozens more.

Nikolas Cruz, 19, pulled a fire alarm and gunned down students with an AR15 assault rifle as they evacuated Marjory Stoneman Douglas High School in Parkland, Florida.

But police were able to use CCTV to identify the shooter and tracked him down to the nearby town of Coral Springs, where he was pinned down and arrested before being taken into custody.

Harrowing footage posted on social media shows terrified pupils crouching under their desks after they barricaded the doors as piercing gunshots are let off just feet away.