The suspect in a shooting spree across Odessa and Midland on Saturday purchased the weapon through a private sale, ABC has confirmed with multiple law enforcement and federal sources.

According to federal law, a private seller may not sell to a person who is flagged, but the seller isn't required to conduct a background check or ask the buyer's status, ABC says.

This private sale loophole is how 36-year-old Seth Aaron Ator purchased the gun authorities say he used to kill seven and wound more than 20 others across a 10-mile stretch of Odessa and Midland, Texas.

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Over the weekend, Gov. Greg Abbott Abbott tweeted that Ator didn't go through a background check for the weapon he used in Odessa, but the governor did not elaborate.

Ator had previously failed a federal background check for a firearm, said John Wester, an agent with the federal Bureau of Alcohol, Tobacco and Firearms. Wester did not say when Ator failed the background check or why.

Officers killed Ator outside a busy Odessa movie theater following a 10-mile stretch of shootings.

The shootings come less than a month after 22 people died in a rampage at a Walmart in El Paso, Texas.

In Texas, a private seller can be charged with a Class A Misdemeanor if they sell a gun to someone knowing they will use it unlawfully. 

A private seller also cannot sell a gun to someone who is intoxicated, at the center of a protective order, or to a felon within 5 years of their release from jail, supervision, or parole. 

If convicted, the seller could face up to a year in jail, a $4,000 fine or both.

Federal investigators are now trying to determine who sold the weapon to Ator. 

The Associated Press contributed to this report.

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