Ted Kaczynski was an American terrorist known as the "Unabomber". He conducted several mail bombings across the United States- killing three Americans and injuring almost two dozen more. Here's a link to the FBI's investigation of Kaczynski. Unabomber - FBI.
He was arrested on April 3, 1996. He was identified after an essay he sent to the FBI was published with the hope that a reader might be able to identify the bomber. His essay was written to bring attention to the effect technology has on society and to speak against the Industrial Revolution and its worsening impact on the environment. The bombings were also meant as a way of getting national attention to the cause. Please don't use this as a means of getting attention to a cause. There are much better (and legal) ways of doing so.