(Photo: Florida Department of Corrections)Manuel Pardo, 56, was convicted of nine counts of first-degree murder in 1988 and was sentenced to death.

A former police officer is to be executed in Florida after being convicted of multiple murders in the 1980s. The former officer is scheduled to be executed on Tuesday, although his attorneys are working at the 11th hour to try and obtain a reprieve.

Fifty-six year old Manuel Pardo was found guilty on nine counts of first degree murder in 1988 and has been on death row for the past 24 years. His attorneys are attempting to argue to the federal court this week that a technicality in the law should mean their client is not executed this week.

The lawyers have said in court on Monday that a recent change in Florida's lethal injection ingredients violates Pardo's civil rights. They allege that the drug combination being used should not be allowed.

Pardo's attorney, William McKinley Hennis III, argued before a judge on Monday that there is a real threat of the lethal drugs being improperly mixed together, resulting in the anesthetic effects potentially being lost. The attorney has raised the concerns as his client will be the first person to be executed using the new combination of drugs.

U.S. Federal judge, Timothy Corrigan, however, has refused to entertain the argument by Hennis, and said the execution would go ahead as scheduled today. However, Hennis has now said that he will appeal the ruling today in one final attempt to postpone the death penalty being enforced.

Lawyers for Pardo have also previously argued that the convict's 1988 trial should never have taken place as he was incompetent to stand trial. However, that argument was also dismissed by the Supreme Court of Florida.

Pardo was fired from the police department after he "falsely testified in court about police corruption in the Bahamas," according to court documents.

Pardo has since said that the stress of losing his job, as well as having an undiagnosed disease, turned him into a killer – but that this person was not who he really was.

Pardo's execution is scheduled to take place at 6 p.m. local time at Florida State Prison in Starke, Florida.