Raoul Moat, the killer who committed suicide last summer at the end of a six-hour stand-off with armed police, was hit by neither of the Taser rounds fired at him by marksmen.
One shot is thought to have embedded itself in his hooded top, while the other landed harmlessly on the ground beside him.
The revelation is likely to prove a major stumbling block to attempts by his relatives to secure compensation.
Moat, 37, a former Tyneside club bouncer, turned his gun on himself on July 10 after being cornered in the village of Rothbury, Northumberland.
A week earlier he had shot and injured his former girlfriend, Samantha Stobbart, 22, in Gateshead, Tyne and Wear, and murdered her new boyfriend, Chris Brown, 29.
The following day he shot and blinded an unarmed policeman, PC David Rathband, 42, on the outskirts of Newcastle.
Moat’s relatives have been seeking a second post mortem after claiming that 50,000-volt Taser blasts may have contributed to his death.
But sources close to the investigation being carried out by the Independent Police Complaints Commission have revealed that neither round caused “any sort of significant” injury to the fugitive.
“There’s some debate over the mark on his arm, but it is highly unlikely to have been caused by the Taser round.
“They are designed to lock on to their target and the rounds are so powerful that in some cases they have had to be surgically removed.
“If it did hit Moat at all it could only have been a very weak, glancing blow. But even that is highly improbable”.
An inquest into Moat’s death was opened and adjourned last month, with a coroner confirming that the killer died from a shot to the head.
The resumed hearing is now expected to be delayed until this summer.
Northumbria Police are confident their firearms officers will be exonerated by the IPCC.
The main focus of the continuing investigation is thought to be the force’s handling of Moat in the days leading up to the final stand-off.
Suggestions that the killer was holed up in a storm drain for most of his time on the run appear to have been discounted by the presence of numerous insect bites on his body.
Police remain convinced that for most of that period he was living wild in local woodland.