Sources close to the inquiry told the Times of London they believe prosecutors will accept a defense plea that the men believed Jean Charles de Menezes, a 27-year-old electrician, was a danger to the public and had to be stopped.
The marksmen told investigators they "honestly believed" de Menezes was a terrorist at the height of the commuter bombing scare and had to use "reasonable force" to stop him from endangering the public.
One Whitehall official said they claim further "they were led by senior officers to believe that he was a terrorist, that he was a suicide bomber."
De Menezes was followed to Stockwell station after the address of an apartment in his building was found at the scene of one of the unexploded bombs left by four suspects July 21.
McPhee, Cokas 'working on their marriage' after affair
Astronomers offer more expansive view of universe