The teenage gunman charged with unleashing one of America’s worst school shootings may have chosen Valentine’s Day to strike after the end of a relationship with a girlfriend.

Nikolas Cruz, 19, described by fellow pupils as a “weird and racist” gun-obsessed loner, has been charged with murdering 17 people at his former school in Parkland, an affluent suburb north of Miami, Florida.

It also emerged that Cruz had previously been treated at a mental health clinic, but was still able to legally purchase an AR-15 rifle, and large amounts of ammunition, passing a background check in February 2017.