Just two days before students in a Texas elementary school were set to begin their summer break, a gunman clad in body armor rushed his way into the school and opened fire on classrooms of young children, killing 19 students and two adults, officials said.

The violent act shook a nation already reeling from another mass shooting across the country just 10 days ago. Parents waited late into the night at a nearby civic center to learn whether their children had survived, with some telling CNN they had to give DNA samples to assist authorities in identifying children.

The 18-year-old gunman, who was killed by law enforcement, is believed to have shot his grandmother before driving to the school to carry out to attack, according to the Texas Department of Public Safety.

As he tried to enter the school, he was engaged by school district police officers, but was still able to enter the building and go into multiple classrooms, DPS Sgt. Erick Estrada said. Authorities say he was armed with a rifle and carrying a backpack.

Tuesday's tragic event marks the deadliest school shooting in nearly a decade since 26 children and adults were killed at Sandy Hook Elementary School in 2012. It is also at least the 30th shooting at a K-12 school in 2022, according to a CNN tally.

In a national address Tuesday night, President Joe Biden recalled the Sandy Hook shooting, which occurred when Biden was serving as vice president.

“I had hoped when I became President I would not have to do this again,” he said. “How many scores of little children who witnessed what happened — see their friends die as if they're in a battlefield, for God's sake. They'll live with it the rest of their lives.”

As the last day of school was drawing near, Robb Elementary students were celebrating with special themed dress days, including Tuesday's theme of “Footloose and Fancy.” Students were encouraged to come dressed in nice outfits and show off their fun footwear, according to a post on the school's Facebook page.

But by Tuesday afternoon, students shaken by a mass tragedy were bussed to a civic center that had been transformed into a reunification site for surviving children and their families. As the evening stretched on, parents of the young victims began to learn their children had not survived the massacre.

“We see people coming out just terrorized. They're crying one by one. They're being told that their child has passed on,” State Sen. Roland Gutierrez told CNN Tuesday night from the civic center.

Here are the latest developments:

Teacher identified as one of the victims: Eva Mireles, a fourth-grade teacher, is among those who was killed, her aunt, Lydia Martinez Delgado, told CNN. According to Mireles’ profile on the Uvalde Consolidated Independent School District website, she had been an educator for 17 years. In her off time, she enjoyed running, hiking, biking, and spending time with her family, according to the website.

Shooter acted alone: The gunman, identified by officials as 18-year-old Salvador Ramos from Uvalde, did not have any assistance, according to Pete Arredondo, chief of police for the Uvalde Consolidated Independent School District.

Gunman shot his grandmother before driving to school: Ramos shot his grandmother in her home before he traveled to Robb Elementary, a DPS spokesperson said. His grandmother was taken to a hospital where she was in critical condition as of Tuesday evening, according to Estrada.

Social media post showed weapons days before massacre: A photo of two AR-15-style rifles was posted to an Instagram account linked to the gunman just three days before the shooting.

“The school year's done,” superintendent says: The Uvalde school district will cancel the rest of its school year, which was scheduled to end Thursday, Hal Harrell, superintendent of Uvalde Consolidated Independent School District said. Grief counseling and support for students will be available at the civic center starting at 10 a.m. Wednesday morning, the district said.

Customs and Border Protection agents responded to the scene: More than 20 CBP agents responded to the shooting and provided aid, a law enforcement official told CNN. One CBP agent was injured and is stable. CBP is the largest federal law enforcement agency in the Uvalde area, which is near the US-Mexico border.