In principal, publicly traded stock has the attribute that all investors make buy and sell decisions on the same information. In order to enforce that, laws prohibit persons who know what is happening within the company before the general public investor knows from profiting specifically from that insider knowledge. There are a lot of restrictions, policies and processes for buying or selling stock "while in possession of material, nonpublic information about the security." [1] There are literally 'black out days' where employees of companies that have stock traded on the public market are prohibited from buying or selling company shares. From my days at a public company, this period was generally 4-6 weeks per quarter, encompassing the quarterly reporting period.

In particular, officers, director and senior staff have to file a form with the SEC in order to trade shares at all. Those trades are subsequently reported to the public in SEC Form 4 [2]. From the SEC [3]:

"Examples of insider trading cases that have been brought by the SEC are cases against:

- Corporate officers, directors, and employees who traded the corporation's securities after learning of significant, confidential corporate developments;

- Friends, business associates, family members, and other "tippees" of such officers, directors, and employees, who traded the securities after receiving such information;

-Employees of law, banking, brokerage and printing firms who were given such information to provide services to the corporation whose securities they traded;

- Government employees who learned of such information because of their employment by the government;

- and Other persons who misappropriated, and took advantage of, confidential information from their employers."

[1] https://www.sec.gov/answers/insider.htm

[2] http://www.nasdaq.com/symbol/tsla/insider-trades

[3] http://ir.tesla.com/secfiling.cfm?filingID=1494730-16-7&CIK=...