Nearly a month after a gunman killed 19 students and two teachers inside Robb Elementary School, shattering a West Texas community, a litany of key questions about the police response remain unanswered. The shifting narrative from state and local leaders in the massacre's aftermath could threaten to exacerbate the trauma for those affected. These types of tragedies can tear communities apart," said John Cohen, a former senior Homeland Security official who is now an ABC News contributor. "One of the ways the healing process can begin is for the community to have a clear understanding of what happened, and of what will be done to prevent something similar from happening again." As families of the victims lay their loved ones to rest, residents of Uvalde continue to hope for answers. They may start to get some on Tuesday, when a Texas House panel convenes to hear testimony regarding the shooting. Since the very first days after the attack, law enforcement officials have said their response was stymied by ... a locked door. But now surveillance video shows that police never tried to open the door. Two months before the mass shooting, the Uvalde school district hosted an all-day training session for local police and other school-based law enforcement officers that was focused on "active shooter response." But basic training protocols - including those involving communication channels and chain of command - went unheeded.