Pharrell Williams is calling for a federal investigation after his cousin was shot dead by police in the US last month.
The Grammy-winning artist's cousin, Donovon Lynch, was killed by police during shootings at Virginia Beach on 26 March.
Williams attended the 25-year-old's funeral this week, which coincided with the star's birthday.
A criminal investigation is ongoing but Pharrell has said there are "too many unanswered city and state questions" and now wants it taken to a federal level.
Mr Lynch was shot and killed after three separate shootings in the Virginia city's oceanfront area.
Deshayla Harris, 28, was also killed alongside Mr Lynch, and at least eight others were injured.
Posting on Instagram, Williams said: "This one is symbolic and a first because I had to speak at my cousin's funeral, and was choked up with emotions. Too many unanswered City and State questions.
"Respectfully, I am calling for a Federal investigation."
Musicians Justin Timberlake, Snoop Dog and Pusha T were among those who paid tribute to Mr Lynch in the comments.
The officer who shot him is on administrative leave.
Police initially said that an officer "encountered an armed citizen" and fatally shot the 25-year-old.
Investigators found a firearm "in the vicinity" of the shooting, with police saying that Mr Lynch had been in possession of a handgun.
The officer who killed Mr Lynch was wearing a body camera, the police chief said, but added that "for unknown reasons" it was not activated.