Authorities have announced on Wednesday that prosecutors will not seek any criminal charges against a Boston officer and an FBI agent who fatally shot a man last year who they believed was plotting an attack against police, .

Suffolk District Attorney Daniel Conley said at a press conference, “the use of deadly force was a lawful exercise of self-defense," .

Usaamah Rahim, 26 years old, was fatally shot June on 2, 2015, in the city's Roslindale neighborhood. Rahim had been under 24-hour surveillance for several months as part of an investigation into his ties with ISIS, that included a plot with two co-conspirators to behead a political activist in New York City, according to authorities.

Conley said that the morning of the shooting, a recorded phone conversation unfurled that Rahim had abandoned his plans to travel to New York and was instead planning to attack officers in Boston. He said, "It was clear from this recorded conversation that Mr. Rahim did not expect to survive this attack".

Conley said that terror investigators approached Rahim at a bus stop, at which point Rahim drew a large, military-style knife from a sheath .

Conley's office reviewed dozens of witness statements and police reports and footage from surveillance cameras. According to Conley the evidence proves that "beyond a reasonable doubt" that Rahim was armed with a knife and "posed the threat of death," .

Rahim was shot three times and taken to a nearby hospital, where he was pronounced dead.

Nicholas Rovinski, of Warwick, Rhode Island, and David Wright, of Everett, Massachusetts, have been facing federal charges they plotted with Rahim to kill civilians in support of ISIS. They have pleaded not guilty.

By Prakriti Neogi