UVALDE, Texas (AP) — Law enforcement authorities faced questions and criticism Thursday over how much time elapsed before they stormed a Texas elementary school classroom and put a stop to the rampage by a gunman who killed 19 children and two teachers.

Texas authorities are holding a press conference at 2:30 p.m. with the latest information. The motive for the massacre—the nation’s deadliest school shooting since Newtown, Connecticut, a decade ago—remains under investigation, with authorities saying that the attacker, 18-year-old Salvador Ramos, had no known criminal or mental health history.

Investigators were also unable to say with any certainty whether an armed school district security officer outside Robb Elementary in the town of Uvalde exchanged fire with Ramos when he first arrived on Tuesday.