[Kartographer]

Where did he get the money? Better than $6000.00 in guns and ammo Wendy’s pays that well?

[Svartalfiar]

Where did he get the money? Better than $6000.00 in guns and ammo Wendy’s pays that well?

Sure. Living at home (with granny), likely paying no rent, buying little to no food, no electricity/water/internet/tv, sounds like he had no car (no payment/insurance), where does his money go? Maybe a cell phone bill, but at 18, granny probably still has him on her plan. ALL of his money is spending money. Easy to save up if that's what he wanted to do with it.

Working Wendy's at say $10 takehome, means 600 hours to get your $6M figure. At a full 40hr week (no OT), it'd take him less than four months to come up with that. 20hr part-time, not even a year.

[US_MilitaryRules]

What brand AR’s did he have that are $3000 bucks each?

[David Chase]

He stole and used his Grandmother’s credit cards.

The rifles alone were approx $2,000 each.

Add mags and ammo total purchase could be around $4,500.

That was probably why the Grandmother and perp had an argument the day of the shooting.
After he shot her, he stole her truck. He didn’t know how to drive because the Grandmother’s husband was going to teach him.
Which explains why he crashed soon after stealing the truck.