Ballou High School sophomore Malek Dayvon Mercer died in June 2015. A District man who fatally shot the 15-year-old youth was acquitted of first-degree murder after he argued during trial that he fired in self-defense. (Courtesy of Sharon Becks)

A District man who fatally shot a 15-year-old youth was acquitted of first-degree murder after he argued during trial that he fired in self-defense after the victim pulled a gun.

The D.C. Superior Court jury, however, could not reach a verdict on a second-degree murder charge and their deliberations ended Monday. Prosecutors will have to decide whether to retry the defendant, 24-year-old Derryck Anjuan Decuir, on that charge.

Prosecutors argued that Decuir was out in the early hours of June 16, 2015, when he spotted Ballou High School sophomore Malek Dayvon Mercer. They said Decuir decided to rob Malek, who was wearing a red Versace belt and expensive Air Force 1 sneakers, and the crime turned deadly. Authorities said Malek was targeted for his belt and sneakers.

As prosecutors prepared for the late February trial, the case seemed an easy one. At least two witnesses had identified Decuir as the shooter. And, after his arrest, Decuir was caught on jail video urging two friends to see about his Stephen Curry jersey and his dog, both of which he said he kept in his back yard. Authorities quickly figured out that he was referring to the Ruger P85 9mm pistol used to kill Malek.

But one day after the trial began, the government learned new details from a key witness, information that would cause its case to crumble, prosecutors said. That witness, a friend of Malek’s, testified that Malek was carrying a shotgun in a backpack the night he was killed.

The testimony bolstered Decuir’s defense. Decuir, who took the witness stand, admitted carrying the pistol in his waistband but told the jury he had it for protection, his attorney said. He said he did not set out to rob Malek, but simply walked by him because he wanted to relieve himself in some nearby trees.

Decuir told jurors that as he passed the teen, Malek reached into his bag and pulled out the shotgun, defense attorneys said. They said Decuir testified that he shot Malek once out of fear.

A young woman who dated Malek’s friend testified that she was with both young men that night. She said she had watched her boyfriend put a large shotgun in Malek’s backpack.

At the shooting scene, the backpack was found with clothes inside. Decuir’s attorneys with the District’s Public Defender Service theorized that Malek’s friend took the gun that had been in the bag and hid it. Prosecutors argued there was no evidence of that.

Following a two-week trial, the jury returned a partial verdict Wednesday, acquitting Decuir of first-degree murder and on the charges associated with robbery. The jury found Decuir guilty of carrying a pistol without a license, obstruction of justice and tampering with evidence.

Jurors were not able to reach a unanimous verdict on the charge of second-degree murder while armed. A judge ruled a mistrial on that count.

In an interview after the trial, one juror said some people on the jury believed that if Malek had a gun, Decuir may have been afraid he would be shot.

Prosecutors and Decuir’s attorneys will return on April 3, at which point prosecutors will decide whether to retry Decuir for second-degree murder. Decuir will remain in the D.C. jail until his next hearing.

Outside the courtroom, Jeffrey Nestler, one of the prosecutors, hugged Malek’s mother, Sharon Becks, and whispered to her, “I’m sorry.”

Becks has repeatedly said her son never carried a gun. Becks and her mother, Sandra Jones, Malek’s grandmother, watched most of the trial. Jones said she and her daughter were “frustrated.”

“We just wanted a verdict,” Jones said.