There have long been concerns about the use of drones for smuggling. The Border Patrol caught two people flying 28 pounds of heroin over the border near Calexico, Calif., in 2015. In July, a man pleaded guilty to attempting to use an unregistered drone to smuggle a bag of marijuana into Autry State Prison in Pelham, Ga.

What drones see can be as worrisome as what they carry. In 2017, a Utah couple was charged with voyeurism for using a drone to spy on people in their bedrooms and bathrooms. One victim chased the drone to a parking lot, found a memory card full of illicit images and turned it over to the police.

When a drone is flown in a crime, it leaves the authorities little to go on — unless they are able to get hold of the machine.

“Drones have a wealth of very valuable forensic evidence to analyze the classic ‘who, what, when, where, why and how, ’ ” said David Kovar, one of a small number of specialists in the new field of drone forensics.

Mr. Kovar and the company he founded, URSA, provide technology to law enforcement officers and train them how to capture data from drones that can establish where and when it was flown and by whom.

But investigators may not be able to tap such expertise in every case. “Unless it is a very high-stakes investigation, it’s unlikely they will call in an expert,” Mr. Holland Michel said.

And even if a drone is recovered and dissected by experts, if it is homemade, it may prove impossible to trace to an owner.