What exactly are the Oregon Arsonists guilty of?

[reACTIONary]

According to the typical news article they claim to have lit the fires to reduce the growth of invasive plants and protect their property from wildfires.

Acording to the Justice Department:

The jury convicted both of the Hammonds of using fire to destroy federal property for a 2001 arson known as the Hardie-Hammond Fire, located in the Steens Mountain Cooperative Management and Protection Area. Witnesses at trial, including a relative of the Hammonds, testified the arson occurred shortly after Steven Hammond and his hunting party illegally slaughtered several deer on BLM property. Jurors were told that Steven Hammond handed out “Strike Anywhere” matches with instructions that they be lit and dropped on the ground because they were going to “light up the whole country on fire.” One witness testified that he barely escaped the eight to ten foot high flames caused by the arson. The fire consumed 139 acres of public land and destroyed all evidence of the game violations. After committing the arson, Steven Hammond called the BLM office in Burns, Oregon and claimed the fire was started on Hammond property to burn off invasive species and had inadvertently burned onto public lands. Dwight and Steven Hammond told one of their relatives to keep his mouth shut and that nobody needed to know about the fire.

http://www.justice.gov/usao-or/pr/eastern-oregon-ranchers-convicted-arson-resentenced-five-years-prison