Since 19 children and two teachers were massacred in Uvalde, Texas, authorities have repeatedly changed their story on what happened before, during and after the bloody siege in two adjoining classrooms.

The May 24 slaughter at Robb Elementary School marked at least the 30th shooting at a K-12 school (kindergarten through high school) so far this year and the deadliest school shooting in nearly a decade.

Now, mourners are tormented by shifting police narratives and the horror of knowing victims were trapped with a gunman for more than an hour — despite repeated 911 calls for help from inside the classrooms.

Here are some of the key details that have changed since the deadly rampage:

More than a week after the massacre, many questions remain unanswered.

Authorities have not said whether 911 calls made by children inside the classrooms were relayed to the incident commander while police waited outside.

It’s also not clear how many of the 21 victims who died may have survived had police entered the classroom sooner.

The Texas Rangers are now investigating the massacre and the law enforcement response. The US Justice Department said it is also reviewing the law enforcement response to the deadly rampage.

A Justice Department spokesperson said the review aims "to provide an independent account of law enforcement actions and responses that day, and to identify lessons learned and best practices to help first responders prepare for and respond to active shooter events.”