Former District of Columbia city council member Sandy Allen shown in 2011 at the intersection of 13th Place and Congress Street SE, where her grandson Jon Allen Jr. was killed. (Marvin Joseph/The Washington Post)

A District man previously convicted of being an accessory in the 2005 shooting death of a former council member’s grandson was sentenced to 50 years in prison Monday for sexually abusing an 11-year-old Maryland girl he met through Instagram.

Robert Kelsey, 29, was found guilty Aug. 29 in a federal trial on three counts of aggravated child sex abuse and transport of a minor for the crime, after the then-26-year-old masked his identity online before picking up the girl from her Prince George’s County elementary school summer camp and raping her in his home on July 25, 2014.

Previously, Kelsey was sentenced to 30 months in prison for being an accessory to the Dec. 31, 2005, shooting death of Jon Allen Jr., 15, a grandson of former D.C. Council member Sandy Allen (D-Ward 8).

Kelsey, then 18, was the driver for a group of youths, including a cousin who fired a burst of shots at a group standing outdoors in the 2400 block of 13th Place SE. Kelsey had complained to his cousin that he had been the victim of an assault, but the shots fired in retaliation killed an unintended target, Allen Jr.

The parents of Jon Allen Jr. shown in 2006: Iris Martin and Jon Allen Sr. (Marvin Joseph/The Washington Post)

Rather than change his conduct after being shown leniency when he was younger, Kelsey “has essentially victimized the community over and over again,” assistant U.S. attorney Andrea Lynn Hertzfeld argued in seeking the 50-year term. “There is nothing left for the court to do but to incapacitate this person” for the bulk of the rest of his life.

The girl’s parents, sisters and mother attended the hearing on Monday, and the victim and her mother addressed the court.

“God says I have to forgive you to move on. But mercy only God can provide to you,” the girl’s mother said, staring down at Kelsey when she finished.

The victim said, “He needs to go away for what he has done, but it is sad he is going to be away from his own daughters.” The Washington Post generally does not identify victims of sexual abuse.

Prosecutors said Kelsey met the girl during the summer of 2014 on Instagram, posing as a 19-year-old and using a fictitious name. They said Kelsey suggested the pair flirt and engage in sex play by text via Kik Messenger and by video via Ovoo.

They said Kelsey lied and claimed he was the victim’s cousin to be able to pick her up from her summer camp. He returned her to the school when the victim learned that her agitated father was waiting at the camp to pick her up and had contacted police after finding out that she had left with a man, prosecutors said.

The girl told her father what had happened, and police traced Kelsey’s phone number and his DNA, prosecutors said.

Kelsey, bearded and his head shaved, apologized to the girl’s family, his family and the court and for “having people go through the trial,” but stood shaking his head in a blue jail sweatsuit as the judge handed down his sentence, which included lifetime supervision as a registered sex offender.

“Obviously you’ve had chances,” said U.S. District Judge Reggie B. Walton of Washington, his voice rising as he went through Kelsey’s conduct.

“You yourself have children, yet you took advantage of this child,” the judge said. “You groomed her. You lied to her. You told her you were a different age. . . . You went into an elementary school. . . . You’re shaking your head, you have no remorse, you don’t accept what you did.”

Walton said the crime was “beyond what society can tolerate,” saying, “a hard sentence is appropriate” and necessary to punish Kelsey and deter others.

Kelsey’s appointed attorney, Christopher M. Davis, acknowledged aspects of the case were “more than troubling,” but asked for a mandatory minimum sentence of 30 years.

Davis said that despite the victim’s testimony, Kelsey was never told that the girl was 11. A nurse who examined her said there was no physical trauma, and the girl said she had been sexually active, Davis wrote.

“The defendant is not a child predator. He has no history of behavior of this nature,” Davis wrote, saying his other convictions were for car theft, fleeing and eluding police.

In the courtroom after the hearing, Kelsey’s father apologized to the girl’s father and family. “I’m sorry. I don’t know what we did,” Kelsey’s father said.

“I forgive you,” the girl’s father told him.