'He had his reasons': Texas school gunman's mother asks victims' families not to judge her son

The mother of the gunman who killed 19 primary school children and two teachers in America's deadliest mass shooting in a decade has said he would have "had his reasons" for committing the atrocity.

Adriana Martínez asked the victims' families to forgive her, and urged them "not to judge" her son.

Salvador Ramos, 18, shot his grandmother before heading to Robb Elementary school armed with a semi-automatic rifle where he entered a classroom and opened fire in the deadliest school attack since 20 children and six adults were killed at Sandy Hook Elementary in Newtown, Connecticut, in 2012.

"I have no words... I don't know what he was thinking," Ms Martínez said.

"He had his reasons for doing what he did and please don't judge him. I only want the children who died to forgive me."

Asked what she could tell the families of those that were killed, she said: "Forgive me, forgive my son, I know he had his reasons."

She did not expand on what these reasons might be.

The gunman barricaded himself in a classroom and opened fire until police eventually broke in and shot him dead.

Uvalde High School, where the gunman was a student, undertook an active shooter drill in March, overseen by the husband of a teacher killed in Tuesday's massacre.

UCISD Officer Ruben Ruiz's wife, fourth-grade teacher Eva Mireles, 44, was shot along her fellow teacher, Irma Garcia and 19 primary school children. Questions have been asked about why police did not storm the school sooner and put a stop to the shooting quicker.