Business Insider reports that according to the complaint, which does not specify whether it was Dzhokhar, 19, or his 26-year-old brother Tamerlan, entered the vehicle and pointed a gun at the victim.
"Did you hear about the Boston explosion?" the carjacker asked. "I did that."
The complaint says the carjacker removed a magazine from the gun, showed the bullet inside, and re-inserted the magazine.
"I am serious," he said.
Dzhokhar Tsarnaev was charged Monday with one count of using and conspiring to use a weapon of mass destruction and one count of malicious destruction of property with an explosive device.
Tsarnaev could face the death penalty.