Story highlights The teens were set to graduate from high school the day after they were killed

Authorities believe the killings were retaliation for a drug robbery one of the victims allegedly committed

(CNN) Three men were arrested Saturday in the shooting deaths of two Maryland teenagers, according to the Montgomery County Police Department.

Shadi Najjar, 17, and Artem Ziberov, 18, were found shot to death in Najjar's blue Honda Civic on June 5, the night before the two were set to graduate from high school.

On Saturday, police arrested Edgar Garcia-Gaona, 24, Roger Garcia, 19, and Jose Ovilson Canales-Yanez, 25, authorities said in a news release.

Officials said 30 shell casings were found at the scene. One of the teens was hit four times, and the other was hit 10 times.

Investigators said they think Najjar and Ziberov were killed in retaliation for a "drug-related robbery" that Najjar allegedly committed months ago.

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