Nathan Dunlap, 38, right, with attorney Madeline Cohen, appears at a hearing at Arapahoe County Court in Centennial, Colo, Wednesday, May 1, 2013. Dunlap's attorneys asked a judge Wednesday to delay designating a week for execution, saying Dunlap's death sentence was meant to be served only after he completed a 75-year sentence for robbery. Dunlap is convicted of killing four people at a Colorado pizza restaurant in 1993. (AP Photo/The Denver Post, Helen H. Richardson, Pool)

AURORA | With Nathan Dunlap’s scheduled execution just three months away, the convicted killer’s lawyers are trying every last-ditch maneuver they can to spare his life.

“We will be trying everything that’s available to us,” said Madeline Cohen, one of Dunlap’s lawyers.

On May 6, the defense formally asked Gov. John Hickenlooper to step in and stop Dunlap’s execution, which a judge last week scheduled for August.

In a 25-page clemency petition, Dunlap’s defense team said his diagnosed bipolar disorder, family history of abuse and mental illness, as well as the flawed way Colorado uses the death penalty mean the governor should let Dunlap spend the rest of his life behind bars.

Cohen said Hickenlooper has a few options, including granting Dunlap’s request to cancel the death sentence and sentence him instead to life in prison without the possibility of parole.

“One thing is certain: Mr. Dunlap will never leave prison alive. It is your decision whether or not he dies at our hands,” the petition said.

Cohen said Hickenlooper also could grant a temporary stay of Dunalp’s execution, pushing the date back for an undetermined length of time. But, she said, the defense is hopeful the governor grants clemency and brings an end to the case that spares Dunlap’s life.

In the clemency petition, the lawyers said Dunlap is sorry for killing four people and wounding a fifth during a 1993 robbery of an Aurora Chuck E. Cheese restaurant.

Dunlap wrote that he is remorseful for what he did as a 19-year-old.

“I’m just sorry for everything that happened on December 14, 1993 and the ripple effect that followed,” he wrote. “As I’ve put my thoughts and feelings to paper, I know saying, writing, and feeling sorry isn’t enough and I wish there was something more that I could do to relieve any pain.”

Several state and federal courts have upheld Dunlap’s death sentence, leaving a plea to the governor as the defense’s only hope of sparing his life.

The defense is also fighting how the Colorado Department of Corrections carries out death sentences, arguing that the secretive nature of the DOC’s procedures violate state law. But two courts have rejected the defense arguments on that front, leaving them with an appeal to the Colorado Supreme Court as likely their only option.

“We will keep exploring all of our options but I think ultimately the governor will have to make a decision,” Cohen said.

The Associated Press reported that Hickenlooper is holding private meetings on the Dunlap case, including meetings with families of the victims who are urging him not to step in. Eric Brown, a spokesman for Gov. Hickenlooper, said the governor is hearing information from all sides.

Prosecutors have said Hickenlooper should stay out of the case. Current district attorney George Brauchler said the governor shouldn’t intervene in a case where a jury and several judges have ruled the death penalty was appropriate.

“Every court who has touched this case has said it has been done correctly,” Brauchler said.