Johnson ran toward Building 12

Dorian Johnson lived at 2928 Caddiefield Road, according to an eviction case against him. He lived in Canfield Green Apartment Complex's Building 12, according to a remark in his grand jury testimony (page 76). That address is in the Building 12's southeast corner. 

Johnson lived at 2928 Caddiefield Road,
in Building 12.

If the run passed through the back, open field, as described by House Repairman, and if Johnson ran home, as he himself testified, then his route was similar to what is depicted in the below photograph.  

Johnson lived in the southeast corner of Building 12.

I speculate that Johnson made contact with the Monte Carlo, which escaped the scene by a similar route. In that meeting, the Monte Carlo's driver and passenger told Johnson what they had seen while watching the final, fatal shots. Johnson himself had not seen those shots, because he had been ducking down in front of the car's passenger seat.