How long does walmart keep their security footage?

About 4 months ago I let my little brother drive my car to walmart while I was passenger. He's too young and I shouldn't of let him. Anyway now he's trying to get me in trouble with my mom because he stole my grandmas car and he's trying to bring up this old incident. My mom said she's going to check security footage of the parking lot. How long does walmart keep their footage? And can anyone just ask to see it or will she need special permission?
How long does walmart keep their security footage?
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