The gunman had purchased a total of 1,657 rounds of ammunition, 315 of which were inside the school, Steven McCraw, director of Texas Department of Public Safety, said Friday.

McCraw said 142 of those rounds were spent cartridges and 173 were live rounds.

Officials found 922 rounds outside of the school, but on school property. Of those rounds, 22 were spent cartridges and 900 were live rounds. Another 422 live rounds were found at the crash site, McCraw said.

The suspect had a total of 60 30-round magazines, 58 of which were at the school. He had fired nearly 200 rounds, most of them inside the school, said McCraw.

Five of the 17 people injured in the elementary school shooting remain in the hospital on Friday, according to officials.

Two children and one adult are being treated at University Hospital in San Antonio, two of whom are in serious condition, and two adults are at Brooke Army Medical Center, both in fair condition.

A 10-year-old girl was discharged from University Health in San Antonio.

Eight children and three adults were treated and discharged from Udalve Medical Center earlier this week.

-ABC News' Jennifer Watts

As part of its ongoing investigation into Tuesday's shooting, the Texas Department of Public Safety is conducting a review of law enforcement actions.

This comes after the visibly shaken Steven McCraw, the director of the Texas Department of Public Safety, revealed a cascading series of police failures before and during one of the deadliest school shootings in the nation’s history.

The incident commander, the chief of Uvalde ISD Police, wrongly believed the incident had transitioned from an active shooter situation to a barricaded subject situation, where the suspect had stopped firing and barricaded himself in a classroom, no longer posing a threat to children, McCraw said.

“He thought there was time,” McCraw said.

McCraw said there may have been a belief by the incident commander that no one was alive anymore inside the classrooms. But, he detailed multiple 911 calls made from inside the classrooms, on which callers explicitly said several children were alive and trapped inside with the shooter. Callers at several points asked for police to be sent in.

-ABC News' Aaron Katersky

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.

When federal agents from Customs and Border Protection and Homeland Security Investigations arrived at Robb Elementary School Tuesday, they immediately encountered a scene of confusion and chaos, according to multiple law enforcement officials briefed on the attack.

Some arrived with heavy equipment, others with whatever they could carry as they ran to the scene on foot.

Initially, these agents, multiple law enforcement sources told ABC News, tried to discern who was doing what, where was shooter who was engaging law enforcement and how were children were being evacuated.

Once the tactical team assembled with enough gear, they became aware of an order not to enter the classroom because they were told the suspect had barricaded himself, the sources told ABC News.

The Texas Department of Public Safety has said the incident commander wrongly believed the shooting had stopped.

Eventually, the special agent-in-charge of Homeland Security Investigations gave the instruction to all federal agents under the umbrella of the Department of Homeland Security that they were free to use their best judgment and to do what they felt was best, the sources said.

The federal agents were unsure whether any children could be saved at that point, but they were interested in evacuating the wounded. Some agents brought children in other classrooms out through windows.

The tactical team went in at 12:50 p.m. CDT and fatally shot the suspect, 77 minutes after the shooting started, officials said.

The suspect was dead at the scene, the sources said. He was found with more than a dozen bullet wounds.