A black iPhone 13 Pro Max was found next to the body of Salvador Ramos after he was shot and killed by a Customs and Border Protection tactical team, according to the search warrant affidavit.
Investigators from the Texas Department of Public Safety sought permission from a judge to analyze the text messages, photos, videos and other "stored communications" on the phone, according to the affidavit, which was first obtained by Houston television station KHOU.
WATCH: 9-year-old says teacher played dead after being shot in Uvalde classroom, recounts seeing gunman
The Texas Rangers, a division of the Texas DPS, is conducting an investigation into the shooting, one of the deadliest in modern U.S. history.
The document also said the two witnesses to the car wreck that preceded the massacre saw Ramos "dressed completely in black with long shoulder-length black hair." The witnesses also told police they saw "the male subject was holding a long rifle and proceeded to load the rifle with a magazine" before he "began to fire multiple gunshots in their direction."
MORE: What we know about 21 Texas school shooting victims; teacher's widower dies of heart attack
The judge authorized investigators to download the contents of the device.
Ramos' grandfather, Rolando Reyes, whose home he was living in at the time of the shooting, told ABC News the suspect had argued with his grandmother over paying a cellphone bill on the morning of the shooting. However, Reyes said he did not believe it was significant. Ramos allegedly shot his grandmother before driving to the school and opening fire.
ABC News has previously reported that authorities have yet to find a specific piece of evidence that explains why the attack occurred May 24 or why Robb Elementary School was the target.
Questions mount over Uvalde police response
Video obtained by ABC News, taken outside Robb Elementary School in Uvalde, Texas, as last week's massacre was unfolding inside, appears to capture a 911 dispatcher alerting officers on scene that they were receiving calls from children who were alive inside the classroom that the gunman had entered -- as law enforcement continued to wait nearly an hour and a half to enter the room.
Texas Sen. Roland Gutierrez said school district police Chief Pete Arredondo was not informed of panicked 911 calls, but ABC News spoke with officials from the Texas Department of Public Safety, who said they cannot confirm this. ABC Owned Television stations initially shared Associated Press reporting on Gutierrez's claims but have since redacted its full report, as the DPS investigation into Arredondo's response is ongoing.
Investigators hope to get more clarity from a follow-up interview with the police chief.
MORE: Video appears to show Texas 911 dispatchers relaying info from kids in Robb Elementary classroom
The Uvalde Police Department and the Uvalde Independent School District police force are no longer cooperating with the Texas Department of Public Safety's investigation into the massacre at Robb Elementary School and the state's review of the law enforcement response, multiple law enforcement sources tell ABC News.
At a news conference last week, Texas DPS Director Steven McGraw said children inside the classroom had called 911 a number of times begging for them to "please send police now." It appeared that information may not have been relayed to officers on the ground, he said.
"That question will be answered," McGraw said when asked directly if the incident commander on the ground received the 911 information. "I'm not going to share the information we have right now. Because I don't have -- I don't have the detailed interview right now."
SEE ALSO: Official says police made 'wrong decision' not to enter Uvalde classroom
But the video obtained by ABC News, taken just outside the premises, appears to show that 911 dispatchers were relaying the information -- including information that the room was "full of victims." It is not clear who on scene, if anyone, heard the calls coming in from the dispatchers.
"Advise we do have a child on the line," an apparent dispatcher can be heard saying in the video.
The dispatcher's information heard on the video appears to match the readout of the 911 calls provided last week by law enforcement officials. McGraw said a child had called 911 saying she was in room 112 and had "advised there were multiple dead."
SEE ALSO: Mass shootings in the U.S. have nearly tripled since 2013, data shows
Later, McGraw said, "she called back and said there's eight to nine students alive."
More than one of the children who dialed 911 from inside the classroom survived, McGraw said on Friday.
Since 2017, mass shootings in the United States -- described as shooting incidents in which at least four people are injured or killed -- have nearly doubled year over year. Already, there have been 212 mass shooting incidents in 2022 -- a 50% increase from 141 shootings in May 2017. The graphic above shows the number of shooting incidents per state. Mobile users: Click here to see our map of mass shootings in the US from the last five years
The number of people injured or killed does not include the suspect or perpetrator. These graphics show the number of victims across all mass shootings from the last five years.
ABC Owned Television Stations contributed to this report.