Video shows the alleged attacker pick up something that fell during the assault, then walk away as if nothing happened. The victim was critically injured after becoming pinned beneath the truck. Witnesses helped him to the sidewalk.
The suspect, whom police identified as a local homeless man, was sitting in front of a restaurant when he suddenly stood and shoved a middle-age pedestrian into the busy road. The attack appeared to happen without provocation.
Minutes before the attack, the suspect made a threatening gesture toward a woman but she saw him lunge and veered away.
Firefighters who saw video of the attack spotted the suspect, who was wearing a distinctive bright jacket, less than an hour later and called police.
"We were going down the right street at the right time and then everything came together and we actually found the individual – the correct person – and turned it over to LAPD," one firefighter told Inside Edition.
The suspect faces an attempted murder charge, while the victim was taken to the hospital with a collapsed lung and several broken bones.