BOSTON (CBS/AP) — A fourth person has been charged in connection with a robbery that left a 21-year-old man dead.

Eighteen-year-old Elijah Charles was arraigned Tuesday in East Boston Municipal Court on charges of armed robbery and armed assault.

Prosecutors say Charles was involved in a Dec. 10 robbery in Boston that led to the shooting of Duncan Ketter.

Authorities say a 16-year-old arranged to buy marijuana from a woman who was joined by Ketter.  After all three got into a vehicle, an armed man emerged from the rear and demanded the pot.

Ketter was shot and allegedly thrown from the vehicle.

Duncan Ketter (Photo Courtesy: GoFundMe, Family Photo)

Charles’s attorney says he is a college student who was asked by an acquaintance to give a ride to pick up marijuana. He says Charles didn’t know of any robbery plans.

The 16-year-old, who has not been identified, was charged with armed robbery in the same incident. Demetrius Cast, 20, of Everett, was charged with armed robbery and other offenses. Thorus O’Brien, 18, of Brockton, was charged with murder, armed robbery, and unlawfully carrying a loaded firearm.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)