The bomb squad checked Mr Wells' body for further explosives
The FBI is investigating the death of a pizza delivery man who said he had been forced to rob a bank by someone who had strapped a bomb to his chest.
Brian Wells had entered a bank in Erie, Pennsylvania, and given staff a note which demanded money and said he had a bomb.
When he left the bank with stolen money he was surrounded by police and told them he had been forced to rob the bank after someone had started a timer on a bomb under his T-shirt.
As the police waited for the bomb squad to arrive the device went off killing Mr Wells.
Erie FBI Special Agent Bob Rudge said a meticulous investigation into the incident would solve the mystery of Mr Wells' death.
"We don't know yet as to why the bomb detonated or how it detonated," Mr Rudge told the Erie Times News newspaper.
"That will be the focus when we get the forensics back," he said.
Mr Wells, 46, had gone to deliver a pizza to an address in a remote area of Erie on Thursday.
About an hour later he turned up outside the bank and left with an undisclosed amount of money.
A local television station captured Mr Wells on camera outside the bank, after he had been handcuffed by police, saying: "Why is nobody trying to come get this thing off me?"
"It's going to go off. I'm not lying."
No-one else was hurt in the explosion.
Erie chief deputy coroner Korac Timon told the AP news agency that the bomb had been hanging from Mr Wells' neck and appeared to be "a very sophisticated device".
Mr Wells' landlady, Linda Payne, said he was a private, trustworthy man.
"I couldn't believe that he would rob a bank," she told AP.
"I think somebody lured him into that place delivering a pizza,
dropped a bomb on him and sent him into the bank."