Joshua Vallum, 29, of Lucedale is the first person prosecuted for a federal hate crime in which the victim was targeted for being transgender, the Justice Department said in a news release.
Vallum knew Mercedes Williamson was a transgender teenage girl when they began dating, but kept her gender identity secret, prosecutors said.
They broke up in 2014 but Vallum decided to kill her in May 2015 because a friend had discovered she was transgender, the Justice Department said.
Vallum, a member of the Almighty Latin Kings and Queens Nation crime gang, feared reprisals from gang members if they found out about the relationship, the Justice Department said.
After luring the 17-year-old into his car under false pretenses, he assaulted her and stabbed her with a pocket knife, prosecutors said. As she tried to flee he stabbed her repeatedly and used a hammer to deliver deadly blows, the Justice Department said.
Vallum initially claimed he killed Williamson in a panic after learning she was transgender.
In his guilty plea to the hate crime on December 21
, he admitted to lying about the circumstances surrounding her death. He would not have killed Williamson if she was not transgender, he said.
Vallum had previously pleaded guilty in state court to murder charges in George County, Mississippi, and was sentenced to life in prison.
Because Mississippi does not have a statute that protects people from bias crimes based on gender identity, the federal government was able to bring federal hate crime charges.
"Today's sentencing reflects the importance of holding individuals accountable when they commit violent acts against transgender individuals," Attorney General Jeff Sessions said. "The Justice Department will continue its efforts to vindicate the rights of those individuals who are affected by bias motivated crimes."
A federal law -- the Matthew Shepard, James Byrd Jr. Hate Crimes Prevention Act -- criminalizes violence based on race, religion, gender, sexual orientation or gender identity. The US attorney's office for the Southern District of Mississippi prosecuted the hate crime.