A Texas lawmaker has formally requested a full FBI investigation into troubling “conflicting accounts” of how police responded to the second-deadliest school shooting in US history.

“I’m calling on the FBI to use their maximum authority to investigate and provide a full report on the timeline, the law enforcement response and how 21 Texans were killed,” Rep. Joaquin Castro said Thursday.

The Democrat shared his letter to FBI Director Christopher Wray making that formal request Thursday, soon after police drastically changed key details about how Salvador Ramos, 18, got into Robb Elementary School and slaughtered 19 kids and two teachers.

“The people of Uvalde, of Texas, and of the nation deserve an accurate account of what transpired,” Castro wrote.

“However, state officials have provided conflicting accounts that are at odds with those provided by witnesses.”

He noted anger over fresh police updates Thursday that contradicted earlier briefings that said Ramos had been confronted by a school cop who “engaged” him outside the school.

He also demanded a detailed timeline of how long it took officers to storm the classroom where Ramos was barricaded inside, as well as the “block of time” Tuesday that “has yet to be fully accounted for.”

He also noted anger at how “parents unsuccessfully urged law enforcement to enter the building during this time and confront the shooter.”

He urged the FBI director to “produce a full, timely, and transparent report on your findings.”

“Your agency must ensure that the American people have a complete and comprehensive account of how this tragedy occurred,” he stressed.