The continuing investigation by local and federal authorities into Sunday's mass church shooting in Nashville shows the suspect legally purchased one of four guns found at the scene of the deadly attack.

A relative of Emanuel Samson — the man accused of opening fire at the Burnette Chapel Church of Christ, killing one churchgoer and injuring seven others — legally purchased the other three firearms, Metro police spokesman Don Aaron said Wednesday.

Police are not releasing the relative's identity but Aaron said the person had been interviewed by law enforcement and reported that the three guns were given to Samson "for safe keeping."

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Law enforcement said Samson had a .40-caliber handgun and 9mm handgun with him in the church and a .22-caliber handgun and semi-automatic AR-15 in his SUV parked outside the building. Police say he fired 12 rounds from the .40-caliber gun, reloading this gun, the only weapon believed to have been used during the shooting.

According to Aaron, Samson bought the .22 caliber semi-automatic pistol from a Rutherford County retailer in December 2015.

His relative, Aaron said, bought the .40-caliber gun — the one Samson used — from a Rutherford County retailer in August 2016

The relative bought the AR-15 from the same Rutherford County retailer as the .40-caliber gun in February 2014 and the 9 mm was purchased from a Wilson County retailer in August 2016.

Although police have confirmed Samson did not have a handgun carry permit, state law allows a person to buy a gun without the permit.

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Retailers are only required to run a background check through the Tennessee Bureau of Investigation on someone who wants to buy a gun from a store, pawn shop or licensed firearm dealer.

This is a developing story. Check back for updates.

Reach Natalie Neysa Alund at nalund@tennessean.com and follow her on Twitter @nataliealund.