It's not so black-and-white as you try to oversimplify a myriad of issues and legalities. It depends. If the man stayed at a reasonable distance, presented ID, approached calmly and slowly and said he needed to check the health of the prisoner because he is both a doctor and required to render aid under Duty to Rescue, and then waited for permission or made his intentions clear if denied, things might've happened differently. Regardless, that jurisdiction is likely to be out a few million to settle this matter and this guy will be slightly richer.
“Citizens may resist unlawful arrest to the point of taking an arresting officer's life if necessary.” Plummer v. State, 136 Ind. 306. This premise was upheld by the Supreme Court of the United States in the case: John Bad Elk v. U.S., 177 U.S. 529. The Court stated: “Where the officer is killed in the course of the disorder which naturally accompanies an attempted arrest that is resisted, the law looks with very different eyes upon the transaction, when the officer had the right to make the arrest, from what it does if the officer had no right. What may be murder in the first case might be nothing more than manslaughter in the other, or the facts might show that no offense had been committed.”
“An arrest made with a defective warrant, or one issued without affidavit, or one that fails to allege a crime is within jurisdiction, and one who is being arrested, may resist arrest and break away. lf the arresting officer is killed by one who is so resisting, the killing will be no more than an involuntary manslaughter.” Housh v. People, 75 111. 491; reaffirmed and quoted in State v. Leach, 7 Conn. 452; State v. Gleason, 32 Kan. 245; Ballard v. State, 43 Ohio 349; State v Rousseau, 241 P. 2d 447; State v. Spaulding, 34 Minn. 3621.
“When a person, being without fault, is in a place where he has a right to be, is violently assaulted, he may, without retreating, repel by force, and if, in the reasonable exercise of his right of self defense, his assailant is killed, he is justified.” Runyan v. State, 57 Ind. 80; Miller v. State, 74 Ind. 1.
“These principles apply as well to an officer attempting to make an arrest, who abuses his authority and transcends the bounds thereof by the use of unnecessary force and violence, as they do to a private individual who unlawfully uses such force and violence.” Jones v. State, 26 Tex. App. I; Beaverts v. State, 4 Tex. App. 1 75; Skidmore v. State, 43 Tex. 93, 903.