Miami, Florida - A 65-year-old man convicted of the rape and murder of his neighbor is to be executed by lethal injection in Florida on Tuesday.

Norman Grim has dropped appeals against his death sentence and is to be executed at 6:00 PM ET at the Florida State Prison in Raiford.

Grim was convicted of the 1998 murder and sexual battery of Cynthia Campbell, a 41-year-old lawyer who lived next door to him.

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There have been 40 executions in the US this year, the most since 2012, when 43 inmates were put to death.

Florida has carried out the most executions, with 14. There have been five each in Alabama and Texas.

Thirty-three of this year's executions have been carried out by lethal injection, two by firing squad, and five by nitrogen hypoxia, which involves pumping nitrogen gas into a face mask, causing the prisoner to suffocate.

The use of nitrogen gas as a method of capital punishment has been denounced by United Nations experts as cruel and inhumane.

The death penalty has been abolished in 23 states, while three others – California, Oregon, and Pennsylvania -- have moratoriums in place.

President Donald Trump is a proponent of capital punishment and, on his first day in office, called for an expansion of its use "for the vilest crimes."