A robber who attached a pipe bomb to a pizza delivery man's neck, killing him when it exploded, has been sentenced to 45 years' jail.

A US court found that in a bizarre robbery attempt, Kenneth Barnes attached the bomb to Brian Wells and sent him with a note to a bank teller.

The judge said at first Wells had been a willing participant, but tried to pull out when he discovered the bomb was real. Barnes forced him to continue at gunpoint.

The bank teller gave the victim the equivalent of about A$13,500 after reading the note.

The bomb later exploded, killing the pizza delivery man, as police officers waited for expert help to arrive, the Associated Press reported.

Barnes has apologised to Wells' family, who insist their relative was never involved in the plot.

It is alleged the robbery was masterminded by a woman named Marjorie Diehl-Armstrong, who is already serving a jail term for murder.