What is exactly is "Citizen's Arrest?"

From our legal history, Great Britain, for the most part, Parliament passed few statutes and instead had the King's (Queen's) judges rule on various disputes both public and private. Often, custom, history, and culture, influenced how the judge ruled. Key figures in understanding the history of common law include Bracton, Coke, and Blackstone. Most of the origin of common law is shrouded in myth and legends about the Anglo-Saxon laws and practices before the Norman conquest. Thus, in English legal history, you had an uncertain Anglo-Saxon practice and custom, layered over with French customs and language, layered over with canon law which was influenced by Roman law.

Because Parliament passed so few laws, in the first wave, Bracton reconciled the practices and customs of alleged Anglo Saxon law with medieval Norman law in the 13th Century. Littleton in about the 15th century focused on developments in land law that represented a large portion of the court's work at the time. Coke, in the 1600's, summarized in his Law Reports and subsequent Institutes, case reports that used both Bracton, Littleton, and "right reasoning" to resolve cases. Coke based his ideas on individual rights under the crown by way of property law summarized in Littleton. Blackstone, shortly before the American Revolution, overlaid the Enlightenment and philosophical interpretations of cases in a systematic replication of Justinian's Code, only with common law. We inherited as a result common law which more or less governed the U.S. practice of law until the codification movements around the 1860's began to take form.

Over time, legislatures and bureaucracies have made statutes and codes primary, based in part on common law ideas, but increasingly becoming more like a civil law system. There are some areas of the law that still have more common law than not; but other areas such as the criminal and commercial codes have become almost wholly reliant on statutes instead of relying on common law precedents.

Civil law countries, by comparison, used Roman law as a foundation, which was last compiled by Emperor Justinian in his code. Justinian's legal scholars made rationality rather than precedent as key. The idea for a civil lawyer is to refer to the source of law as inspiration rather than particular cases. Cases are used to illustrate the legal principles in the code rather than as a source for development of the law. Development of the law is to be left to those with authority to make law (legislators or kings, not judges.

Might find this link on common law useful. https://digitalcommons.law.yale.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=3959&context=fss_papers

 

Ok, again, try to provide the relevant legal code and/or caselaw;

I bolded sections that applied to the particular situation video that you witnessed to help in determining what the language means. California, probably due to its population, has a quite sophisticated section of criminal code addressing arrests by officers, public officials, and private citizens. Far more than a lot of states, California's code has quite a bit of statutory provisions covering arrests by private persons aka citizen's arrest. There was quite a bit extra in the code dealing with arrests by private persons but those were outside the scope of what you were discussing. So, if you want to discuss the relevant California laws regarding citizen's arrest and why it is related to the THR's legal forum limits discussing citizen's arrest in the context of firearms, please do so.


California Code, Penal Code - PEN § 834
ARREST DEFINED.  BY WHOM DEFINED.  An arrest is taking a person into custody, in a case and in the manner authorized by law.  An arrest may be made by a peace officer or by a private person.

California Code, Penal Code - PEN § 835

An arrest is made by an actual restraint of the person, or by submission to the custody of an officer.  The person arrested may be subjected to such restraint as is reasonable for his arrest and detention.

California Code, Penal Code - PEN § 837
ARRESTS BY PRIVATE PERSONS.  A private person may arrest another:

1. For a public offense committed or attempted in his presence.

2. When the person arrested has committed a felony, although not in his presence.

3. When a felony has been in fact committed, and he has reasonable cause for believing the person arrested to have committed it.

California Code, Penal Code - PEN § 840
An arrest for the commission of a felony may be made on any day and at any time of the day or night.  An arrest for the commission of a misdemeanor or an infraction cannot be made between the hours of 10 o'clock p.m. of any day and 6 o'clock a.m. of the succeeding day, unless:

(1) The arrest is made without a warrant pursuant to Section 836 or 837 .

(2) The arrest is made in a public place.

(3) The arrest is made when the person is in custody pursuant to another lawful arrest.

(4) The arrest is made pursuant to a warrant which, for good cause shown, directs that it may be served at any time of the day or night.

California Code, Penal Code - PEN § 841
The person making the arrest must inform the person to be arrested of the intention to arrest him, of the cause of the arrest, and the authority to make it, except when the person making the arrest has reasonable cause to believe that the person to be arrested is actually engaged in the commission of or an attempt to commit an offense, or the person to be arrested is pursued immediately after its commission, or after an escape.

The person making the arrest must, on request of the person he is arresting, inform the latter of the offense for which he is being arrested.

California Code, Penal Code - PEN § 847
(a) A private person who has arrested another for the commission of a public offense must, without unnecessary delay, take the person arrested before a magistrate, or deliver him or her to a peace officer.

(b) There shall be no civil liability on the part of, and no cause of action shall arise against, any peace officer or federal criminal investigator or law enforcement officer described in subdivision (a) or (d) of Section 830.8 , acting within the scope of his or her authority, for false arrest or false imprisonment arising out of any arrest under any of the following circumstances:

(1) The arrest was lawful, or the peace officer, at the time of the arrest, had reasonable cause to believe the arrest was lawful.

(2) The arrest was made pursuant to a charge made, upon reasonable cause, of the commission of a felony by the person to be arrested.

(3) The arrest was made pursuant to the requirements of Section 142 , 837 , 838 , or 839 .

 

Note, if you read search engine results, you would have come up with a quite succinct guide to California's caselaw delving into citizen's arrests.
This publication is from the Alameda County District Attorney's Office
http://le.alcoda.org/publications/files/CITIZENSARREST.pdf

 

I think that we are done here unless someone has a specific instance of their state and specific instances of cases or statutes that pertains to the issue and citizen use of firearms in a self defense situation. If so, send me a PM to reopen it with your specific questions.

This is a very complicated subject that varies significantly across state lines--much of the case law involves off duty officers or officers working out of jurisdiction. Another portion addresses loss prevention officers in commercial establishments. None of these particulars concern the average private citizen.
Needless to say, there are significant legal issues for the private citizen involved apart from the rather risky tactical decision to detain someone.