(CNN) -- The Idaho Department of Fish and Game has launched an investigation into a taunting letter, apparently written by a poacher.
The man who called himself 'Poacher X' sent in a picture of a deer that he said he killed -- and promised to do more hunting.
"Here is a picture of the nice buck I poached up in northern Idaho this year," he wrote on the back of the photograph, "& I plan to do all my Idaho hunting like this from now on. & I'll send a picture of my nice pronghorn next. Also my turkey."
Chris Wright with the fish and game department told CNN affiliate KBOI that it was the first time in his 15-year law enforcement career he had seen "somebody turn themselves in, in this manner, calling themselves 'Poacher X.'"
The return address on the letter said only 'Poacher X' with a postmark from Everett, Washington.
His agency suspects 'Poacher X' is angry at the out-of-state fees for hunting licenses and tags that run between $300 to $500, Wright told the television station.
The department only catches 1 percent of poachers in the state, the station said.
Early this month, the agency was investigating a poaching incident in which a group of teens shot five deers, killing four.
And in October, the agency asked for help from the public in identifying those responsible for illegally killing a moose and a bull.