While anti-Koch and anti-Walker activists cheered the prank, there is a serious argument to be made that the "prank" was a crime under Wisconsin law.
Wisconsin law protects the "personal identifying information" of individuals. The term is broadly defined, and includes a person's name:
(b) "Personal identifying information" means any of the following information:The misappropriation of such "personal identifying information" is a felony if done for purposes listed in the statute, including obtaining anything of value or benefit, or to harm the reputation of the person whose name was misappropriated.
1. An individual's name.
(2) Whoever, for any of the following purposes, intentionally uses,any personal identifying information or personal identification document of an individual, including a deceased individual, without the authorization or consent of the individual and by representing that he or she is the individual, that he or she is acting with the authorization or consent of the individual, or that the information or document belongs to him or her is guilty of a Class H felony: attempts to use, or possesses with intent to use
(a) To obtain credit, money, goods, services, employment, or any other thing of value or benefit.
(b) To avoid civil or criminal process or penalty.
(c) To harm the reputation, property, person, or estate of the individual.The Wisconsin Supreme Court recently upheld the validity of the statute against a First Amendment challenge, State v. Baron (2009) 769 N.W.2d 34, 318 Wis. 2d 60. (I do think the section of the law as to harming reputation has unanswered First Amendment issues which were not addressed by the Baron case.)
The terms "benefit" and "value" also have been held to convey their normal and usual meaning, and not to require that the victim suffer a financial loss. State v. Lis (App. 2008) 751 N.W.2d 891, 311 Wis.2d 691.
There certainly is a good argument to be made that the "prank" fits the definition of identity theft.
There does not seem to be any doubt that the blogger used Koch's name without authority or consent. The blogger thereby used Koch's "personal identifying information."
The purpose of the use of Koch's name also was to obtain a "benefit" for the blogger, namely access to Gov. Walker, and to obtain something "of value," namely a recording to be used by the blogger.
Additionally, it appears that there also was the purpose of harming the reputation of Koch, both through the inflammatory statements by the blogger acting as Koch and by creating the appearance of some improper influence by Koch on the political process.
In sum, there certainly seems to be enough evidence already known at least to justify an investigation by the Madison police as to the possible theft of David Koch's identity, a felony under state law.
Instead, the Madison Police Chief wants an investigation of Gov. Walker, even though there were no statements made by Walker which could constitute a crime. If the Madison Police Chief wants someone and something to investigate, it is not Gov. Walker.