By Heide Brandes

OKLAHOMA CITY (Reuters) - Oklahoma is set on Tuesday to execute by lethal injection a man convicted of stabbing an elderly couple to death during a robbery in 2000 that netted about $73, some of which he and convicted accomplices used to buy tacos.

James Lewis DeRosa, 36, is scheduled to be executed on Tuesday evening at a state prison, according to the Oklahoma Department of Corrections. He would be the second inmate executed in Oklahoma this year and the 16th in the United States.

DeRosa was convicted of killing Curtis Plummer, 73, and Gloria Plummer, 70, of Poteau, Oklahoma, while robbing their home. DeRosa was sentenced to death in October 2001, authorities said.

According to trial testimony, DeRosa was employed for a short time by the Plummers and had told several friends they would be an easy target to rob. Eric Castleberry, then 21, and Scotty White, then 18, agreed to help.

White drove DeRosa and Castleberry to the Plummers' house, according to court documents. After the Plummers let them inside, DeRosa and Castleberry pulled knives and DeRosa stabbed them multiple times each and slit their throats.

DeRosa and Castleberry ransacked the house looking for cash and other valuables, ultimately taking about $73 in cash and the couple's pickup truck, which they left in a nearby lake, according to court documents.

The two met White afterward, and after disposing of the bloody knife and clothes, used some of the money to buy tacos, according to court documents.

Castleberry testified at DeRosa's trial in exchange for a sentence of life without parole, and White was charged with accessory after the fact to murder and received two 25-year prison sentences, the last seven years on probation, according to the Oklahoma Department of Corrections.

(Editing by David Bailey and Dan Grebler)