Is the money the questioner received as a result of a car accident, which involved bribes, false testimonies, and amounts exceeding necessary compensations, lawful (halal) or unlawful (haram)? And must the excess amount be returned to its owner?

What you have done encompasses several prohibitions: lying and bearing false witness, both of which are major sins. Paying money in exchange for these false testimonies is considered prohibited bribery, and "the Prophet, peace and blessings be upon him, cursed the briber and the bribed." It also involves consuming people's wealth unlawfully, for anything beyond what you are entitled to is illicit gain. It is obligatory upon you to repent, feel remorse, and seek forgiveness, return the excess amount beyond your entitlement to the person concerned and ask for their forgiveness, and command the bribed doctor and officer to repent.