Johnson ran to the Monte Carlo because its doors opened

After Dorian Johnson gathered the cigarillos from the police vehicle's roof and then from Michael Brown's left hand, Johnson immediately ran away laughing on the street's south side. 

MC Passenger initially watched Johnson, not the police vehicle. MC Passenger watched Johnson run away on the street's south side and then saw Johnson stop in front of 9391 Canfield Drive, far behind the Monte Carlo. 

Then a loud noise prompted Johnson to stop and then run across the street and prompted MC Passenger switch his attention from Johnson forward again to the police vehicle. 

After the first gunshot was fired inside the police vehicle, the Monte Carlo moved slowly backwards, and both doors were opened wide. Johnson immediately ran toward the Monte Carlo. He reached the Monte Carlo at about the same time as the second gunshot was fired. Within a few seconds, MC Passenger moved into the back seat, and Johnson climbed in and hid in front of its passenger seat. 

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About 7:30 minutes earlier, at about 11:54:30 along West Florissant Avenue, MC Passenger had opened the same passenger-side door of the same white Monte Carlo to invite Johnson and Brown to climb in for a ride. Now at 12:02:00, Johnson climbed in again. 

MC Passenger's decision on Canfield Drive that both car doors should be opened wide would be inexplicable to almost everyone else. Most people in such a situation would close their car windows and lock their car doors -- not open their car doors wide. 

When the second gunshot was fired, Johnson was crouching next to the Monte Carlo as Brown ran past. According to Johnson, Brown yelled at him, "Keep running, bro'". Police Officer Darren Wilson still had not appeared from behind his police vehicle. During these moments, Johnson could have run away in various directions. Instead, he stayed by the Monte Carlo, which was no more than eight feet from the police vehicle, and asked to get in. 

A few seconds after the second gunshot, Wilson appeared. He came around the police vehicle's back end and ran down the middle of Canfield Drive, chasing Brown. As soon as Wilson ran past, Johnson could have run away in various directions. 

The reason why Johnson did not run away was that he got into the Monte Carlo and hid down in front of the passenger seat.