A third teenager has been arrested and charged in the shooting death of a University of Massachusetts student who was working as a congressional intern in Washington, D.C. last summer. 

Eric Tarpinian-Jachym, 21, of Granby, Massachusetts, was an innocent bystander when he was shot four times near the convention center in Washington on June 30. Investigators say three armed suspects exited a stolen vehicle and began firing shots at two young men. 

Tarpinian-Jachym was rushed to the hospital where he died the next day. Five other people were assaulted or injured in the incident, prosecutors said. 

On Wednesday night, 18-year-old Naqwan Antonio Lucas of the District of Columbia, was arrested in Montgomery Village, Maryland and charged in Tarpinian-Jachym's murder. 

Last month, 17-year-old Kelvin Thomas, Jr. and Naqwan Lucas' brother, 17-year-old Jailen Lucas, were arrested and charged as adults on counts of first-degree murder while armed in connection with Tarpinian-Jachym's murder. 

Tarpinian-Jachym was a rising senior at UMass Amherst and was spending the summer in Washington as a congressional intern for Rep. Ron Estes, a Republican from Kansas. 

Naqwan Lucas pleaded not guilty at his arraignment in D.C. Superior Court on Thursday afternoon. He is being held until a status hearing with his co-defendants on November 7. 

Naqwan Lucas was also charged in the July 4 murder of 17-year-old Zoey Kelley, who was found dead of a gunshot wound to the head in a bedroom closet of an apartment in Washington, D.C. 

Last week, the Metropolitan Police Department and FBI announced a $75,000 reward for information leading to Lucas' arrest.