Delivery driver or package thief? It could be harder than ever to differentiate the two, thanks to an expanding delivery program from the online retail giant Amazon.

It's called Amazon Flex and it's where private, freelance drivers, deliver right to your doorstep.

Amazon Flex launched in Seattle in 2015 and is now in more than 30 other metropolitan areas, including the Valley. Drivers pick-up packages from an Amazon warehouse, then deliver them to your door in their own vehicles.

That's where the confusion with package thieves can come in.

In Sacramento, Steve Rutledge learned this firsthand when his letter carrier was suspicious of a car full of packages driving around his neighborhood.

"Before he had a chance to get any closer to the vehicle, the driver ran up to the front porch of a house, ran back to the vehicle, and took off," Rutledge said.

It turns out, that was no package thief -- a growing crime that's already affected more than 23 million Americans -- but an Amazon Flex driver. A reported 80 million Americans subscribe to Amazon Prime. As Amazon Prime's subscribers exponentially increase, so does the demand to deliver packages quickly.

Amazon is hoping its Flex drivers meet that demand. They make $18 to $25 an hour and although they don't have an official delivery vehicle like the traditional delivery services, they do have to pass criminal and driving background checks.

So the next time you see someone running with a package near a porch, it could be a delivery driver, not a thief.