Rolando Reyes, 72, the gunman's grandfather, told ABC News he had no idea his grandson had purchased two AR-15-style rifles or that they were in his house.

Since Reyes is a felon, it is illegal for him to live in a house with firearms. Reyes said he would have turned his grandson in.

Reyes said there were no signs the morning of the shooting that anything unusual was going to happen. The suspect had a minor argument with his grandmother over the payment of a phone bill, but nothing significant.

The suspect lived in a front room and slept on a mattress on the floor, according to Reyes. The suspect had been staying with his grandparents after having a falling out with his mother.

Reyes said he took the suspect to work sometimes and that he was very quiet, but he did not seem violent. Reyes also said he tried to encourage his grandson to go to school but the suspect would typically just shrug in response.

Reyes said the suspect did not know how to drive and did not have a driver's license. Reyes also wondered how his grandson would have even gone to purchase the weapons or if he trained on the weapons, saying someone must have taken him there.

The suspect's grandmother, who he shot in the forehead, is undergoing surgery on Wednesday. Reyes said he believes she will survive.

-ABC News' Matt Gutman

Salvador Ramos, the suspect in the Robb Elementary School shooting, after turning 18 on May 16, purchased two rifles and carried out the second-worst school shooting in U.S. history within the span of eight days, according to multiple law enforcement officials.

The suspect purchased two AR-15-style rifles on May 22, two days before the massacre and six days after his birthday, multiple law enforcement officials told ABC News. They were legal purchases.

Once the shooter made entry into a classroom he barricaded himself and opened fire, according to the sources.

Officers from the Uvalde Police Department and agents from Customs and Border Protection entered into the classroom and immediately took fire from the gunman before they shot and killed him.

Investigators are going through the ballistics to determine who fired the fatal shot.

Ukrainian President Volodymyr Zelenskyy offered his condolences to the families of the victims of the shooting on Twitter.

"Deeply saddened by the news of the murder of innocent children in Texas. Sincere condolences to the families of the victims, the people of the US and @POTUS over this tragedy," Zelenskyy said in a tweet.

Zelenskyy added: "The people of Ukraine share the pain of the relatives and friends of the victims and all Americans."

Actor Matthew McConaughey decried the shooting in his hometown of Uvalde, Texas.

"We have tragically proven that we are failing to be responsible for the rights our freedoms grant us," he wrote in a statement on Twitter.

"We cannot exhale once again, make excuses, and accept these tragic realities as the status quo."

Those inside a classroom with the shooter made several calls to 911, but the tactical unit that arrived at 12:15 p.m. waited 35 minutes before breaching the classroom, Steven McCraw, director of Texas Department of Public Safety, said at a press conference Friday.

A 911 call was made at 12:03 p.m. from room 112 and lasted 23 seconds. McCraw did not identify the caller.

She called back at 12:10 p.m. and advised that there were multiple dead in the classroom, McCraw said.

The person then called again at 12:13 p.m. and again at 12:16 p.m., when said there were eight to nine students who were still alive, McCraw said.

A call was made by someone else from room 111 at 12:19 p.m., the caller hung up when another student told her to hang up, McCraw said.

At 12:21 p.m., three shots were heard over a 911 call. At 12:36 p.m., another 911 call was made by the initial caller and it lasted for 21 seconds. The student caller was told to stay on the line and be very quiet. She told 911 that the gunman shot the door, McCraw said.

At approximately 12:43 p.m. and 12:47 p.m., she asked 911 to please send the police now, McCraw said.

The caller said she could hear police next door at 12:46 p.m. At 12:50 p.m., the Border Patrol tactical unit finally breached the door and shot the suspect.