A US jury on Friday failed to agree on the death penalty for the gunman who stormed a Colorado movie theater and killed 12 people, effectively condemning him to life in prison.

The sentence will be formally imposed by a judge at a later hearing, but the jury said for each of the 12 counts: "We the jury do not have a unanimous final sentencing verdict on this count and... understand the court will impose a sentence of life imprisonment without the possibility of parole."