(CNN) The West Texas man who killed seven people and wounded 25 in a shooting rampage bought his gun in a private sale, which doesn't require a background check, a law enforcement official told CNN.

Police have described the firearm Seth Ator, 36, used in Saturday's killing spree in and around Odessa, Texas, as an AR-15-style rifle.

Ator tried to buy a firearm on January 14, 2014, but wasn't allowed to, the Texas Department of Public Safety told CNN in an email.

The department is prohibited by law from disclosing the reason he was denied the purchase, the DPS said.

Ator failed a background check when he applied to get a gun, a representative for the Bureau of Alcohol, Tobacco, Firearms and Explosives said Monday, without giving details.

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