(CNN) Police have arrested a suspect in connection with the death of 7-year-old Jazmine Barnes, and they're giving credit to a tip from social activist and writer Shaun King.

The arrest of Eric Black Jr. -- who said he was driving the vehicle used in the shooting -- came as a result of a tip King received and sent to Harris County Sheriff Ed Gonzalez, the sheriff said Sunday.

"He became a target in our investigation based on a tip that initially went to journalist and activist Shaun King," Gonzalez told reporters. "Mr. King then passed that tip to me personally."

Two days after Jazmine's death, King turned to his legion of Twitter followers to enlist their help in finding her killer and offered a reward of $25,000 for information. S. Lee Merritt, an attorney advising Jazmine's family, also joined the cause. The reward eventually climbed to $100,000.

On Wednesday evening King had tweeted he had combed through hundreds of tips. "Mostly garbage," he said. "All well meaning. 3-4 helpful. Working with the family and local authorities. Some promising leads, but not nearly enough."

Shaun King

Gonzalez said Sunday that one of King's tips "provided a much different angle to what we were initially looking at," alluding to the fact authorities initially said the suspect was a white man in his 40s driving a red pickup truck. Black is a 20-year-old African-American man. The white man in the red truck was likely just a witness, the sheriff told reporters.

Black was pulled over for not using his turn signal and was subsequently arrested for possessing marijuana, per an affidavit read in court. Investigators identified Black as one of two suspects an anonymous tipster said were involved in the shooting.

He was arrested and is expected to be formally charged with capital murder on Monday. Authorities have not released information on the suspected shooter, who Black said opened fire from the passenger seat.

A mugshot of Eric Black Jr. was released by the Harris County Sheriffís Office.

"I want to thank again Shaun King for his activism and help and raising awareness and the monies that were put forward to be able to generate those calls," Gonzalez said.

The shooting is believed to be a case of mistaken identity.

It was still dark out the morning the shooting occurred, Gonzalez pointed out, and Jazmine's mother and sisters had just gone through a traumatic experience, which could have affected their perception of those devastating moments.

King said Sunday morning on Twitter that he shared the tip with Gonzalez's office on Thursday. He also said the white man in the red truck described by eyewitnesses was not the shooter and probably fearing for his life.

King and Merritt, the civil rights attorney, have been friends since meeting about 20 years ago at Morehouse College, a historically black school in Atlanta. They've worked on several cases together over the years, including the killing of Antwon Rose II, a black teenager killed by police outside Pittsburgh in June.

Merritt also told CNN he and King helped authorities identify the suspects who attacked a black man, DeAndre Harris, at the Unite the Right rally in Charlottesville, Virginia, in August 2017.