Buying explosive precursors together does not automatically trigger any sort of investigation.

I bought acetone, hydrogen peroxide (in the form of a wood bleaching kit), and hydrochloric acid together in 2002 at a Home Depot and never got the slightest bit of attention.

I also bought an 80 pound sack of ammonium nitrate from a fertilizer dealer in 2002 with cash. I didn't show ID. The employees didn't grill me at all. I was pretty surprised, actually. I thought there would be some sort of tracking in place six years after the OKC bombing and 1 year after the 9/11 attacks. Maybe they only start tracking when you try to buy it by the tonne. Maybe my appearance (clean shaven white guy with glasses, no tattoos) gave me a pass where other sorts of buyers might need to show ID or explain why they're buying.