Under a reprieve, Dunlap could conceivably be executed one day. The reprieve will stay in force until Hickenlooper or another governor lifts it.
Hickenlooper said Colorado's capital punishment system is flawed, citing a study that showed the death penalty was sought and imposed inconsistently.
He also said the state doesn't have the drugs in place to carry out an execution by lethal injection, and that many states and nations are repealing the death penalty.
Hickenlooper said he granted a reprieve instead of clemency because he saw the question before him as being about the use of the death penalty, not about Dunlap.
Dunlap was convicted in 1996 of ambushing and killing four employees at a Denver-area Chuck E. Cheese restaurant. The jury sentenced him to die. His last guaranteed appeal was rejected this year.
His execution was scheduled for the week of Aug. 18.
Prosecutors have said Dunlap should be executed because he had shown no remorse and had bragged about the killings.
Dunlap's attorneys said that he was remorseful, and they released a video and written statement in which Dunlap apologized.
They also said he had undiagnosed bipolar disorder at the time of the shootings.
Copyright 2013 The Associated Press.