"The defendant stated once inside the store, he opened fire using his AK-47, shooting multiple victims", according to the affidavit, The Washington Post reported.
The document describes the suspect getting out of his auto with his hands up and saying "I'm the shooter" when he was stopped by an officer near the crime scene.
"I'm the shooter", Crusius told the arresting officers as he got out of the vehicle with his hands in the air.
A racist, anti-immigrant manifesto believed by authorities to have been written by the suspect was posted online shortly before the attack, which the author called a "response to the Hispanic invasion of Texas".
More on this as it develops.
A spokesman for police in Allen, Texas, says a record has been found of a telephone call to police that attorney's for Patrick Crusius' family say came from his mother. In all, eight of the dead in the Texas border town were Mexican nationals.
Cryotherapy mishap cause of Brown's foot injuries
Brown was benched for a crucial Week 17 game for missing practice, and the Steelers traded him to Oakland for a third round pick. While they're poised to make big improvements this season, much of it will be reliant on their No. 1 wide receiver's health.
Meanwhile, several victims of the El Paso attack and another mass shooting which took place in OH less than 24 hours later and left nine people dead were being laid to rest.
Once arrested and charged, Crusius was booked into the El Paso County Jail, where he remains with no bond set.
She was transferred to a public safety officer who told her that based on her description of the situation, the man was legally allowed to purchase the weapon.
Earlier this week, the mother of the suspect had called the police and expressed concern about his son owning an assault rifle weeks before the shooting took place. In a statement provided to several media outlets, the family said, "Patrick's actions were apparently influenced and informed by people we do not know, and from ideas and beliefs we do not accept or condone".
Police say Crusius, who lived near Dallas, drove more than 10 hours to the largely Latino border city in Texas to carry out the shooting that killed 22 people and wounded about two dozen others.
Attempts to reach Crusius' family have been unsuccessful.
Additionally, US Attorney John Bash said the Justice Department is "seriously considering" bringing federal hate crime and federal firearm charges.