(AP) — Pepper-sprayed customers, smash-and-grab looters and bloody scenes in the shopping aisles. How did Black Friday devolve into this?

As reports of shopping-related violence rolled in this week from Los Angeles to New York, experts say a volatile mix of desperate retailers and cutthroat marketing has hyped the traditional post-Thanksgiving sales to more dangerous levels.

With stores opening earlier, bargain-obsessed shoppers often are sleep-deprived and short-tempered. Arriving in darkness, they also find themselves vulnerable to savvy parking-lot muggers.

Add in the online-coupon phenomenon, which feeds the psychological hunger for finding impossible bargains, and you’ve got a recipe for trouble, experts say.