The jury on Thursday sentenced Brian Richardson to life in prison without release after deliberating about two days.
Richardson was convicted last month of the July 2007 killing of Steven Obara, a 60-year-old who authorities say was targeted because he was a child molester.
Prosecutors argued the death penalty was the only way to punish Richardson for the cold-blooded murder. Defense lawyers maintain that Richardson was mentally ill at the time and urged a jury to grant him mercy so he could seek redemption.
Richardson could have been the first person sentenced to death in federal court since June 2011.