Make sure the baby raccoon is an orphan
If the baby is found clinging to or within several feet of the dead adult, the baby is likely orphaned. Only the female raccoon cares for her young, so if the mother is killed the baby will require care from a wildlife rehabilitator.
However, it is possible for several raccoon mothers to have babies near each other, so a dead raccoon found in the area (like down the street but not right beside the baby) may not be related. If there is any uncertainty, you should try to reunite the baby with its mother before seeking help.