Texas school shooter Salvador Ramos posted about attack on Facebook

Chilling details emerged Wednesday of how teenage maniac Salvador Ramos slaughtered 19 children and two teachers — including how he bragged about his sick plans on social media.

Ramos, who turned 18 last week, started posting on Facebook “approximately 30 minutes before reaching the school,” Gov. Greg Abbott said of the “demented person” who brought “evil” to Uvalde.

“The first post .. said, ‘I’m going to shoot my grandmother.’ The second post was, ‘I shot my grandmother,’” Abbott said of Ramos’ critically injured 66-year-old relative, Cecilia, who was medevaced to a San Antonio hospital.

“The third post, maybe less than 15 minutes before arriving at the school was, ‘I’m going to shoot an elementary school,’” Abbott said.

Despite being shot, the grandma “was able to run across the street to a neighbor and get help,” Texas Department of Public Safety Director Steve McCraw also told the press conference.

However, her deranged grandson — who did not have a drivers license — had already taken her vehicle and driven the nearly three miles to Robb Elementary School, where he crashed and fled, the officials said.

“He took a backpack with one rifle with him,” McCraw said, confirming it was a Daniel Defense weapon, one of two that Ramos had bought the previous week in a local sporting goods store along with 335 rounds.

He had bought the first on Tuesday last week — the day after turning 18, and exactly a week before he was shot dead after one of the deadliest school shootings in US history.

After crashing his grandma’s vehicle, Ramos went to the west side of the school building, where there is a back door, McCraw said of the high-school dropout who had no known criminal history.

There, a “brave” school resource officer “approached him” and “engaged him” — but “gunfire was not exchanged,” McCraw said, without elaborating on why.

Instead, Ramos then made it into the school, running down a hallway to two adjoining classrooms, the official revealed.

“And that’s where the carnage began,” McCraw said.

Arriving officers then “engaged him” and were able to “keep him pinned down in that location,” he said — with a SWAT team of Border Patrol agents backing up local police. One of the border agents is the one who gunned down Ramos, officials said.

“They breached the classroom door, they went in, engaged Ramos and killed them at the scene,” he said.

The official appeared emotional as he addressed possible failings by the officers he otherwise hailed as heroes.

“Obviously, this is situation we failed in the sense that we didn’t prevent this mass attack,” he conceded.

“But I can tell you those officers that arrived on the scene and put their lives in danger — they saved other kids.. They kept him pinned down,” he insisted, saying they were “very proud” of that.

It was a message shared by the governor, who said the bloodbath “could have been worse” without the officers’ response.

Follow The Post’s live coverage of the Texas elementary school shooting

“The reason it was not worse is because law enforcement officials did what they do. They showed amazing courage by running toward gunfire for the singular purpose of trying to save lives,” the governor said.

“They were able to save lives. Unfortunately, not enough,” he said.