Federal prosecutors (don't know a better word, in English, for this) are asking Brazilian Air force about the presence of VANT (non-tripulated airplanes, drones) on the area, if is there any missing, and so on.
It's based on pictures of the debris of the accident, where something that looks like the wheel of on e specific model is shown.
In portuguese:
the classified request for information,
some blog post about it
A better picture of the probable drone