Stacey Kelly had to take long pauses to manage her emotions and wipe tears.

It is the one-year anniversary of the death of her son, 28-year-old Karl Sellers Jr. and homicide investigators are still mystified.

"I just instantly went numb," she said as she recalled the phone calls from detectives on November 14, 2016.

Her son had been found murdered in the stairwell of an apartment building at 5027 57th Avenue in Bladensburg, Md.

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Kelly was surrounded by family as she spoke about the torture of not knowing why her son was murdered.

Karl Sellers Jr. was a beloved father of two elementary aged kids. He was an outgoing bike messenger in D.C.

"He was the first to go on those bikes with no brakes," Kelly smiled as she recalled.

So called "fixies" for brakeless fixed-gear, direct-drive bikes became a trend in the cycling world.

He was shot to death at 10:17 p.m. after leaving an apartment where he was visiting a friend.

The attack was so unexpected, at first rescuers thought it was a medical emergency when they found him in the stairwell of the building.

Sellers had no beefs, no run-ins with the wrong people, no real enemies, as far as his family and investigators know.

It was as if he had been targeted for an assassination for no reason at all.

Prince George's County Police have not given up. They were canvassing the apartment complex to try and jog memories in October. But detectives remain mystified.

"This is one where the smallest tip really might help," said Cpl. Ryan Hunter.

Prince George's county police solve 80 percent of the homicides they investigate. Investigators credit community cooperation and tips for the high rate.

In this case, they are appealing to the community again.

"Maybe someone remembers a vehicle out of place, or even the color of a car," Hunter said. "That might be all it takes."

As will all crimes, anyone can give tips completely anonymously in Prince George's County.

In the Sellers case, a reward is being offered.

Callers wishing to remain ANONYMOUS may call Crime Solvers at 1-866-411-TIPS (8477) or textPGPD plus your tip to CRIMES(274637). Tips can also be given online.