A 23-year-old Northwest man was sentenced to 40 years in prison Wednesday for the 2010 fatal shooting of his 16-year-old friend.

Raymond Roseboro was convicted in February of first-degree murder and other charges in the Nov. 30, 2010, death of Prince Okorie. It took prosecutors three trials to convict him; two attempts ended in mistrials after juries couldn’t reach a unanimous verdict.

On Wednesday in D.C. Superior Court, Roseboro again proclaimed his innocence. His wrists and ankles shackled, he turned to Okorie’s mother and told her that someone else killed her only son.

“I never disrespected you. I walked him home from school when others kids teased him. He was my heart. I didn’t kill him. I didn’t pull the trigger,” Roseboro said.

Prosecutors never revealed a motive. At a preliminary court hearing weeks after Roseboro’s arrest, a D.C. homicide detective testified that Roseboro thought Okorie had cooperated with authorities and identified a friend of Roseboro’s in the fatal shooting of Neil Godleski, a student at Catholic University.

Judge Russell F. Canan didn’t allow prosecutors to present that theory to jurors, ruling that there wasn’t enough evidence. But he appeared to put stock in it at Wednesday’s sentencing.

“Other than children and the elderly, the most protected class are witnesses,” Canan said, describing the slaying as “senseless and cowardly.”

Authorities later said that Okorie had not been cooperating.

Scholar Okorie, the victim’s mother, sobbed loudly during the sentencing, despite efforts of relatives and members of her church to console her. At one point, the judge called for a break to allow her to compose herself.

Roseboro’s mother, other relatives and friends sat on the other side of the courtroom.

When Scholar Okorie returned to the courtroom, she slowly walked up to the bench and handed her cellphone to the judge to show off her newborn grandson. She told the judge that she emigrated from Nigeria for a “better life” for her family. Two daughters were in college when their younger brother was killed.

“I wanted my children to be like Obama,” she told the judge. And then she turned to Roseboro. “You took my son. And you killed me the day you killed my son,” she said. “I am a Christian, so I forgive you. But I will never forget.”

During his trials, Roseboro told jurors that he was at his mother’s home with his girlfriend when Okorie was killed. But in the third trial, Roseboro’s then-girlfriend took the witness stand and contradicted his alibi.

Prosecutors also presented cellphone records that appeared to show Roseboro’s girlfriend repeatedly calling him on his cellphone at the time of the shooting. Evidence, prosecutors said, that the two were not together.

Roseboro faced a mandatory minimum of 30 years in prison, but Canan gave him more because Roseboro was under supervision by the Department of Youth Rehabilitation Services at the time of the shooting. As a teenager, Roseboro was arrested in connection with a cellphone robbery in which the victim’s jaw was severely broken, the judge said.

Canan also added time because Roseboro lied under oath during his trials.