( CNN ) -- A former Florida police officer convicted of multiple murders in the 1980s is scheduled to be executed Tuesday , and his attorneys are still working to save his life . Manuel Pardo , 56 , was convicted of nine counts of first-degree murder in 1988 and was sentenced to death . Pardo 's attorneys argued in federal court Monday that Florida 's recent change in the drug combination it uses for lethal injections would violate their client 's civil rights . Attorney William McKinley Hennis III told U.S. Judge Timothy Corrigan that if the drugs were to be improperly mixed , the anesthetic effects would be compromised . `` Manny Pardo would be the first inmate to be executed using that new lethal injection protocol , '' Hennis said . Corrigan denied the complaint , and Hennis said he would appeal the ruling . In another legal filing , the Supreme Court of Florida denied Pardo 's argument that he should have never been tried in 1988 because he was incompetent to stand trial . David Waksman , who prosecuted the case , dismissed the claim , saying , `` He was just a cold-blooded killer who used to be a cop . '' Pardo 's life started on the other side of the law , according to court documents filed by his attorneys . At age 17 , he enlisted in the Navy and served honorably served from 1974 to 1978 . In 1981 , Pardo re-enlisted in the Marines and remained a reservist while he worked for the Florida Highway Patrol and the Sweetwater , Florida , Police Department . In 1985 Pardo was fired from the police department and left the reserves when , according to court documents , `` he falsely testified in court about police corruption in the Bahamas . '' Hennis said the stress of losing his job , compounded with a serious undiagnosed disease , turned him into `` someone he was not , '' a killer . During his trial , Pardo took the stand and admitted to the murders . `` He came up with this vigilante story , '' recalls Waksman . `` He said , ' I 'm ridding the community of this vermin and technically it is not murder because they 're not human beings . ' '' The only chance Pardo has to win on the competency issue is if the United States Supreme Court decides to hear his appeal . The execution is scheduled for 6 p.m. Tuesday at Florida State Prison in Starke , Florida . Read more : Life sentence closes oldest cold case . Read more : MS-13 gang member gets 76 years . Read more : Bus driver acquitted after 2011 New York crash .
Hennis , Tuesday was convicted of nine murders in Sweetwater in the 1980s . Sentenced to death , he is scheduled to be executed on the 1980s . His attorneys continue to appeal on competency and civil rights grounds .