The glass on a Dallas firetruck was shattered Friday by an unknown object, Dallas police now say.
Dallas Fire-Rescue's Engine 19 was driving down Interstate 30 near Munger Boulevard when one of its windows shattered.
The firefighters on board thought they had been hit by a rock, but during the course of the investigation they found reason to believe it was something other than a rock that shattered the window.
Dallas police originally told NBC 5 that the glass had been hit by a bullet, though later backed off of that statement and said they were unable to confirm that information.
Just after 2 p.m., police said the police department's crime scene response unit found no evidence a bullet or projectile shattered the glass.
Exactly what caused the glass to break remains a mystery.
None of the firefighters were injured and they were not headed to an emergency when the glass shattered.