The fifth member of the "Texas 7" gang, a group of seven prisoners who escaped prison in 2000, is set to be executed on Thursday evening. His attorneys, however, have objected to the execution saying that 57-year-old Patrick Murphy did not fatally shoot a suburban Dallas police officer during a Christmas Eve robbery over 18 years ago.

The seven prisoners had earlier successfully escaped from the John B. Connally Unit near Kenedy, Texas, on December 13, 2000. Six of the seven members were eventually apprehended days later during a robbery attempt where they shot and killed a police officer Aubrey Wright Hawkins. One of the members committed suicide before he could be rearrested. The inmates were arrested a month after the killing in Colorado, ending a six-week manhunt.

Four of the remaining members have since been executed. The fifth member, Murphy, is slated to receive a lethal injection at the state penitentiary in Huntsville, while the execution date for the sixth inmate, Randy Halprin, has not been assigned yet.

Officer Hawkins, in 2001, had just finished Christmas Eve dinner with his family when he responded to a call about a robbery at a sporting goods store. The officer who had been with the Irving police for nearly 14 months, rushed to the spot where he was ambushed by the Texas 7 and shot 11 times, leading to his death.

This undated photo provided by the Texas Department of Criminal Justice shows Patrick Murphy. Lawyers for the member of the notorious "Texas 7" gang of escaped prisoners who is scheduled to be executed Thursday, March 28, 2019, say he should be spared because he never fatally shot a suburban Dallas police officer during a Christmas Eve robbery nearly 18 years earlier. Murphy is slated to die by lethal injection after 6 p.m. at the state penitentiary in Huntsville. (Texas Department of Criminal Justice via AP)

Murphy is set to be the third inmate to put to death in Texas, the nation's busiest capital punishment state, and fourth in the United States, according to the AP. Reports state that Murphy was convicted under Texas' law of parties, according to which, a person is criminally responsible for the actions of another if they engaged in a conspiracy.

The 57-year-old's attorneys, however, have filed appeals in an attempt to stop his execution. They have argued that Murphy's death sentence is unconstitutional because he was the lookout during the robbery and was not a prime participant in the crime. The lawyers, David Dow, and Jeff Newberry, have claimed that their client had left the scene even before the shooting began.

"It is unconscionable that Patrick Murphy may be executed for a murder he did not commit that resulted from a robbery in which he did not participate," the attorneys in a statement said.

Mugshots of wanted armed convicts, who escaped from Connally Unit Prison, December 13, 2000. The escapees are suspected of killing Police Officer Aubrey Hawkins by shooting him 13 times and running him over in a Christmas Eve robbery at a sporting goods store in Irving, Texas, near Dallas. Local and state police and federal agents have offered a reward of $100,000 per escapee. The convicts are top row L-R; Joseph C. Garcia, Randy Ethan Halprin, Larry Jame Harper and Patrick Henry Murphy, Jr. Bottom row, L-R; Donald Keith Newbury, George Rivas and Michael Anthony Rodriguez. (Getty Images)

The Texas 7 gang's reported leader at the time of the prison breakout was 30-year-old George Rivas, who was serving 18 consecutive 15-to-life sentences. Another member Michael Anthony Rodriguez, 38, was serving a 99-to-life term for contracting the murder of his wife by Rolando Ruiz Jr. While Larry James Harper, 37, Joseph Garcia, 29, and Patrick Henry Murphy Jr., 39, were all serving 50-year sentences. The longest rap sheet of the group belonged to Donald Keith Newbury who was serving a 99-year sentence. The youngest member of the group, Randy Halprin, 23, was serving a 30-year sentence for injury to a child.

Frontal and profile view of inmate Donald Keith Newbury during his incarceration in a Texas prison. Seven armed convicts, who escaped from a Texas prison December 13, 2000 are suspected of shooting a policeman 11 times in a Christmas Eve robbery near Dallas. (Getty Images)

The seven inmates used multiple well-planned ploys, overpowered and restrained nine civilian maintenance supervisors including their boss, four correctional officers, and three uninvolved inmates at approximately 11:20 am on December 13, 2000. The inmates planned the escape during lunch when there was less surveillance of certain locations. They reportedly impersonated prison officers on the phone and stole clothing, credit cards and identification from their victims. The offenders disguised in stolen civilian clothes pretended to be on the premises to install video monitors. All the seven inmates then stole a prison maintenance pick-up truck and drove away from the prison.

Murphy, who became a Buddhist during his time in prison, has now asked that his death be stalled until prison officials allow his spiritual advisor, a Buddhist priest, to be present during his last hours. His lawyers have alleged that by going ahead with the scheduled execution they are violating Murphy’s First Amendment right to freedom of religion.

Gary Johnson, Director of the Texas Department of Criminal Justice Institutional Division, speaks to the press January 11, 2001 in Austin, Texas after a report was released about seven escaped convicts who are still at large. (Getty Images)

A federal judge in Houston and the 5th U.S. Circuit Court of Appeals in New Orleans reportedly turned down Murphy's request this week.

The lead prosecutor who handled the Texas 7 case, Toby Shook, refuted the attorneys' claims and said that Murphy actively participated in the robbery, monitored a police scanner from a getaway vehicle and alerted the other inmates when Hawkins was approaching the store. “He alerted them. That allowed them to set up their ambush,” Shook said.

Murphy's lawyers have also argued to stop his execution because Texas lawmakers are currently debating over the controversial law of parties and whether to change the law to prohibit a death sentence for a person convicted as a co-conspirator, reports state.