The killing of Michael Brown was "a blatant assassination," Ty Pruitt, the cousin of the black teenager shot by a police officer in Missouri, told Good Morning Britain, after an autopsy revealed he was shot six times, twice in the head.
Mr Pruitt said: "My question is, as far as policemen go, your training tells you to first stun, that's why you carry a stun gun...if he was that much of a threat, why didn't you just stun him, then subdue him?"
Unrest sparked by Mr Brown's death is ongoing in Ferguson, a suburb of St. Louis.
Mr Pruitt called for the peaceful protesters to "stand firm," but said to the looters and "the people who provoke violence - 'Go home...every time the cops have to come out and deal with you it pushes my cousin's case backwards.'"
More top news
An Irish nanny freed after baby murder charges in the US were dropped describes her 'nightmare' and branded the prosecution a 'scandal'.
A man became so frustrated with noise from a nearby building site that he shot a builder with an air rifle, police say.
A backbench revolt over proposals to ease purdah restrictions on the EU referendum has led to a government climb down.