For birth in the human realm it is always a kusala kamma done in the past which conditions the patisandhi citta (rebirth consciousness). Which kamma conditions it depends on many factors - but it is only one kamma. It might be one very strong kamma or it might be habitual kamma that has the opportunity to be the condition.
If one did some major akusala kamma like killing a parent then that is so strong that it will condition rebirth in hell in the next life. King Ajatasattu killed his father Bimbisara but later studied Dhamma and ws a great supporter of the Sangha - he even had his builders prepare the place where the 500 arahats rehearsed the teachings at the first council. Despite so much meritorious deeds he was reborn in hell. However the Commentary says he will become a PaccekkaBuddha in a future life.