The NAACP Legal Defense and Educational Fund called for an independent investigation of the shooting death of Joshua Brown, who was a witness in the case of former Dallas police officer Amber Guyger, as his slaying Friday touched off an outcry around the country.

Brown's death came days after Guyger, a white officer who was off duty, was convicted and sentenced to 10 years for murder in the death of Botham Jean, a black man whom Guyger shot in his own apartment last year. After Brown was fatally shot at an apartment complex on Cedar Springs Road, some raised questions about whether the shooting was tied to his testimony.

Dallas Police Chief U. Reneé Hall said on Sunday the department did not have a suspect or motive in Brown's death. Monday, a spokeswoman for the department declined to comment on the calls for an independent investigation.

Sherrilyn Ifill, president of the NAACP Legal Defense and Educational Fund, said state or federal authorities should take over the investigation in a statement released Sunday evening.

“The circumstances surrounding the murder of Mr. Brown cries out for answers,” Ifill said in a statement. “Most importantly, it demands an independent investigation of how and why he was killed.”

The department did not immediately respond Monday to a request for comment regarding the calls for an independent investigation.

Hall said in a statement on Sunday the department would handle the investigation.

"We are committed to solving this case and will work diligently to apprehend the individuals responsible for Brown’s death,” Hall said in a written statement.

Brown’s family declined to comment on Monday to a request for a comment regarding the investigation.

Officers were called Friday night to the Atera apartments in the 4600 block of Cedar Springs Road, where witnesses reported hearing gunshots and seeing a silver four-door sedan speed out of the parking lot.

The department confirmed Sunday afternoon that the 28-year-old Brown was the victim whom officers found at about 10:30 p.m. Friday with multiple gunshot wounds to his lower body. He died after being taken to Parkland Memorial Hospital.

Staff writer Dana Branham contributed to report.

How to contact police about the case

Anyone with information about the shooting may contact Detective Jacob White at 214-671-3690 or email jacob.white@dallascityhall.com and refer to the case number, 202433-2019.

Crime Stoppers will pay up to $5,000 for information leading to an arrest and indictment in this case. To make an anonymous tip, call 214-373-8477.

Bill Perkins, an author and the CEO of the BrisaMax Holdings consulting firm, is offering a $100,000 reward to find whoever killed Brown, civil rights activist Shaun King announced Sunday.