Boston police shot and killed a man on Tuesday claiming he approached them with a knife when they attempted to question him for a terror related investigation.
Federal Bureau of Investigation (FBI) later said the man, Usaamah Rahim, was under 24-hour surveillance as part of an investigation but did not give further details on the case.
"We believed he was a threat," Boston Police Superintendent William Evans said.
"The level of alarm brought us to question him today. I don't think anyone expected the reaction we got out of him."
Police claimed they warned the suspect to drop his knife and retreat before shooting him after he continued to advance.
Authorities’ account of the case was challenged by Ibrahim Rahim who in a Facebook post said his brother was shot while waiting for a bus to go to work.
"This morning while at the bus stop in Boston, my youngest brother Usaamah Rahim was waiting for the bus to go to his job. He was confronted by three Boston Police officers and subsequently shot in the back three times," Rahim wrote in his Facebook page.
Police claim witness accounts and a video of the incident confirm the suspect had a knife and advancing on officers before they shoot them.