Sept. 17 (UPI) -- A Florida man convicted more than 30 years ago in the murder of three Mulberry residents was executed Wednesday evening, the Florida Department of Corrections announced.

David Joseph Pittman, 63, died at 6:12 p.m. in the lethal injection at Florida State Prison in Raiford, the corrections department said.

The U.S. Supreme Court and Florida Supreme Court declined to intervene in the execution, which Pittman's lawyers appealed on the grounds of intellectual disability.

In 1991, Pittman was convicted of the 1990 murders of three members of his estranged wife's family in Mulberry after he stabbed them and set their house on fire. Prosecutors said Pittman murdered his wife's family after she filed for divorce.

According to officials, the bodies of 60-year-old Clarence Knowles was located in the living room of the home. His wife, Barbara Knowles, 50, was found in a hallway and their 21-year-old daughter, Bonnie Knowles, in a bedroom.

Pittman's death marked the 12th execution carried out by Florida this year, a record for the state, according to USA Today. The state has two more executions scheduled for later this year.

Many elected officials and anti-capital punishment advocates throughout the United States have been calling for an end to capital punishment recently.

Scores of religious leaders and U.S. veteran groups have argued that, despite convictions and the penalty's finality, it's still a manifestly cruel and unfair punishment in Florida in many current cases.

Meanwhile, the group Floridians for Alternatives to the Death Penalty argued that Pittman grew up in "extreme poverty" with a mother who "gleefully admitted" to whipping him with a belt from the time he was 4-years-old, they said, adding, "sometimes every day."

"His family could not afford to continue the psychiatric treatment he needed. Violence, neglect, and hardship shaped his childhood long before the state ever called him 'defendant,'" they told The Ledger.