KANSAS CITY, Mo. — The prosecutor for St. Louis said Thursday she won’t be charging two officers in the fatal shooting of a black 18-year-old last year, concluding that no evidence disproves police explanations that it was self-defense.

Calling Mansur Ball-Bey’s August 2015 death ‘‘a tragedy in every aspect of the word,’’ Circuit Attorney Jennifer Joyce said the officers and a witness reported that an armed Ball-Bey ran from a home during a drug and gun raid. Both officers, who are white, have said they fired at Ball-Bey at the same time after he pointed a gun at one of them, though one officer missed, according to Joyce.

Joyce, whose office investigated the shooting separately from an internal police probe, said Ball-Bey’s loaded gun was found at the scene, with his palm print on the ammunition clip.

A local medical examiner concluded that Ball-Bey sustained a severed spinal cord and a bullet pierced his heart.

‘‘One of the biggest challenges we face in this case is that there is no independent, credible witness we can put in front of a grand jury or regular jury who contradicts police statements,’’ Joyce said in a statement. ‘‘None of the other witnesses had a clear view at the moment when Ball-Bey was shot.’’

She noted that the officers declined to speak to prosecutors.

An attorney for Ball-Bey’s family, Jermaine Wooten, has questioned the police account that Ball-Bey was armed.

Ball-Bey’s death came a little more than a year after a white police officer, Darren Wilson, shot and killed Michael Brown, a black, unarmed 18-year-old, in nearby Ferguson, Mo.

Associated Press