Tyler Holder pleaded guilty to the murder of Alanna Gallagher and to the attempted capital murder of an Arlington, Texas, police officer who was shot while trying to make the arrest last year. He was given a 40-year sentence for the shooting, consecutive to his life sentence.
The Tarrant County District Attorney's Office said Holder will not be eligible for parole for at least 50 years.
"Today a dangerous killer was brought to justice," Deputy Chief District Attorney Bob Gill said in a statement. "Tyler Holder will never pose a danger to another child. The family of Alanna Gallagher and Officer Charles Lodatto are very satisfied with this resolution of the cases."
Holder was 17 when he killed Alanna in 2013. Prosecutors said they decided against trying him for capital murder because of Supreme Court decisions that bar death sentences for juveniles and automatic sentences of life with no parole.
Alanna disappeared while playing near her home in Saginaw, a Fort Worth suburb. Her body was found about a mile away July 1, 2013, stuffed in a black trash bag with a silver-colored tarp covering her head.
Investigators said she had been sexually assaulted.
Holder was arrested after DNA found on items with the body matched his.
He also admitted setting a fire at the Gallagher house and the arson of a car days after the killing. He received an additional 20 -year concurrent sentence.