Let's assume for a moment that DEW exist, what physical properties would this weapon need to have in order to be responsible for the alleged damage?

Microwaves can't heat plastic, but neither can stones, and metal can't be heated easily as well. For microwaves to work, they need a liquid medium, such as water in a piece of meat. Or water in a tree?

but you say that trees are not affected, so they probably won't be microwaves.

Possibly laser beams? A laser can heat objects, whether something starts to burn depends proportionally on the energy supplied, if a material can distribute the supplied energy faster than the laser can supply it, the object will not burn! This applies to all objects, including trees and especially plastic, but you claim it was not as affected as stone, metal and other materials that conduct heat well. Ok now let's assume that it's magically possible with DEW to set something on fire, how much energy would this weapon take to, say, set a car or house on fire?

To heat 1 liter of water from 0° to 100° takes 1kwH. now let's convert that to a house, and then to all houses and all cars, and everything you think was affected, and now my question, where do you store this amount of energy for a single DEW.