one of the victims suffered critical head trauma as the stage fell half-way through a song during a sold-out showing of american pie .
the performers plummeted through the wooden riser in a spectacle so unbelievable that some audience members initially believed it was choreographed .
nicola gruszka , a student who was singing in front of the stage when the platform behind her gave way , said , adding that students ` really came together as a unit in that moment ' .
more than 12 people were hurt and least one person was critically injured , a spokesman for the westfield police department said on thursday evening .