Human rights group Amnesty International is trying to convince the Governor of the US State of Virginia to reduce the sentence of a Jamaican man who is due to be executed today.
Edward Nathaniel Bell, 44, has been convicted of the 1999 murder of a police officer.
Prosecutors said Bell shot the sergeant in the face because he feared the officer would find him carrying a gun or drugs.
Amnesty International is claiming that Bell was convicted despite woefully deficient legal representation and serious questions about his guilt.
It also claims Bell might be mentally retarded.
The European Union has also asked the Virginia governor to exercise mercy.
Bell's execution was previously delayed because the US Supreme Court was considering concerns about lethal injection procedures.
However, in April last year, the court ruled that the execution method was acceptable.