According to Det Garcia, Mr Crusius waived his right to a lawyer, and told them that he had travelled from the suburbs of Dallas with an assault rifle and multiple magazines containing ammunition.
CNN is reaching out to El Paso police and a defense attorney for Crusius for comment about Garcia's account. A public safety officer allegedly told her that he was legally allowed to purchase the weapon and did not pursue any additional information about her concerns; attorneys said she did not provide her name or her son's name.
The El Paso shooting suspect's mother called the Allen, Texas, Police Department weeks before the shooting because she was concerned about her son owning an "AK" type firearm, lawyers for the family confirmed to CNN.
On Thursday, lawyers for Mr Crusius told USA media that his mother had called police weeks before the attack to say she was concerned about him owning a weapon.
Patrick was 20-years-old when the call was made.
Authorities believe Crusius posted a racist online screed that railed against an influx of Hispanics into the USA shortly before the attack.
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Rain & storms likely tonight into Sunday morning
Wednesday: Partly cloudy with a few showers and thunderstorm especially in the morning, highs in the middle 80s. Up to three-quarters of an inch of rain is expected with more falling during thunderstorms.
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Authorities said Crusius drove 11 hours from his hometown of Allen, Tex., near Dallas, to perpetrate a massacre in the predominantly Hispanic city of El Paso. They then saw a man - identified as Patrick Crusius, the 21-year-old charged with capital murder in the case - get out of the vehicle with his hands in the air, the affidavit said.
"This was not a volatile, explosive, erratic behaving kid", said Chris Ayres. Federal officials have called the attack - which also injured dozens of people - domestic terrorism and said they are weighing federal hate crimes charges in the case.
The attack came hours before another mass shooting in Dayton, Ohio, in which nine people were killed.
President Donald Trump and other lawmakers have suggested so-called red flag laws as a way to prevent mass shootings.
But some gun rights advocates say allowing law enforcement to take firearms would go against the USA constitution, which protects the right to bear arms.
Trump said Friday that he believes he has influence to rally Republicans around stronger federal background check laws. Add El Paso Shooting as an interest to stay up to date on the latest El Paso Shooting news, video, and analysis from ABC News.