Sources: Uvalde gunman had argument over cell phone before shooting

UVALDE, Texas (CBSDFW.COM) — One day after the Robb Elementary gunman turned 18, he legally purchased an assault rifle. Three days later, he bought a second, with 375 rounds of ammunition.

In an Instagram account linked to the shooter, a picture was posted of two assault riles four days before the school shooting that killed 21 victims, including 19 children.

READ MORE: 'I am going to shoot an elementary school', Uvalde suspect allegedly messaged before shooting

Family friends say the teen — identified as Salvador Ramos — stopped going to school this year and neighbors say his anger seemed to grow when he didn't graduate.

Two months ago, after an argument with his mother, Ramos went to go live with his grandmother. His mother's boyfriend said they had no idea he had bought any weapons, and thought he was doing better when he went to live with his grandmother.

READ MORE: Texas families looking for answers after Uvalde shooting

"I don't know, sir. I don't know what happened. I don't know where he got all the guns. I just saw it on the news," Juan Alverez said.

Alverez said Ramos and his mother argued a lot, but the argument that caused him to go live with his grandmother was an argument over the use of WiFi on his mother's phone.

On the day of the shooting, law enforcement sources said Ramos had an argument with his grandmother about a cell phone.