Killian served in the United States Army as part of the Tennessee National Guard from 1970 until 1973, when he received an honorable discharge as a corporal.

[1] On May 20, 2010 Killian was nominated by President Barack Obama to be the United States Attorney for the Eastern District of Tennessee.

[2] He was reported favorably by the United States Senate Committee on the Judiciary on September 23, 2010.

He was confirmed by the full United States Senate by voice vote on September 29, 2010.

[4] Killian prosecuted a case on the basis of "public safety concerns" in which a convict, Edward Young, touched shotgun shells while helping a recently-widowed neighbor sort through her deceased husband's belongings; Young was subsequently sentenced to a mandatory minimum of fifteen years in federal prison.