Following are brief explanations of those five cases:

INPEX OFFERING

On March 21, the SESC recommended a 50,000 yen ($640) fine against Chuo Mitsui Asset Trust and Banking for trading on inside information on an around $6 billion share sale by energy firm Inpex (>> INPEX Corp) in July 2010. The SESC said a fund manager at Chuo Mitsui sold existing shares in Inpex and took out short positions after being tipped off by a brokerage employee. While the SESC did not name the broker, it was widely reported that a junior saleswoman at Nomura Securities was the source of the leak.

Altogether, the trades generated a profit of 14 million yen for his fund. The fine was calculated using a pre-set formula based on the expected commission gained and not on the profit generated, in line with the SESC's fining system.

Nomura, a lead underwriter on the offering, issued a statement saying it was cooperating with the investigation and expressing regret over the incident. It did not publicly acknowledge it was the source of the leak until June.

NIKKO SMBC LEAKS TO RETAIL CLIENTS

On April 13, the SESC called for Nikko SMBC Securities, Japan's third-largest broker, to be punished for leaking information about a public stock offering to its retail clients before the deal was officially announced. The SESC said directors at Nikko SMBC passed on word of the offering to at least 21 sales branches without carrying out the proper internal procedures to control the information flow.

At eight of those branches a total of 23 sales staff tipped off 34 clients, mostly individual investors, to prime them to buy the shares once the deal was officially launched, violating the financial instruments law, the SESC said.

While the SESC did not name the stock issue in question, sources with knowledge of the matter said it was the roughly $12 billion offering by Sumitomo Mitsui Financial Group (>> Sumitomo Mitsui Fin.), Nikko's parent, in early 2010. On April 20, the Financial Services Agency (FSA) issued Nikko SMBC with an order to take steps to bolster its internal controls and clarify management responsibility.

MIZUHO FINANCIAL OFFERING

On May 29, the SESC recommended an 80,000 yen fine against Sumitomo Mitsui Trust for insider trading ahead of the roughly $9 billion share offering of Mizuho Financial Group (>> Mizuho Financial Gr.) before it was announced in June 2010.

It was the second case to involve Nomura, with two of the brokerage's employees the suspected source of the leak. Nomura was the lead manager on the offering.

NIPPON SHEET GLASS OFFERING

Also on May 29, the SESC sought a 130,000 yen fine against Japanese hedge fund Asuka Asset Management for insider trading ahead of the roughly $500 million stock offering of Nippon Sheet Glass (>> Nippon Sheet Glas) before it was announced in August 2010.

Sources with knowledge of the matter said an employee at the Tokyo office of JP Morgan Chase & Co (>> JPMorgan Chase & Co.) was the source of the leak, marking the first time that a foreign bank had been ensnared in the probe. Asuka, which manages money for Japanese pensions and other institutional investors, said one of its fund managers had been involved in the insider trading.

TEPCO OFFERING

On June 8, the SESC recommended a fine of 14.68 million yen against First New York Securities for insider trading on the roughly $6 billion share offering by Tokyo Electric Power Co (>> Tokyo Elec. Power) before it was announced in September 2010.

It marked the first penalty against a foreign firm in the probe, and was a product of coordination with the U.S. Securities and Exchange Commission (SEC). It was also the third case linked to Nomura, the sole underwriter on the offering.

The fine came to about twice the profit First New York had gained from taking a short position on Tokyo Electric one day before the offering was announced, and then buying the stock back at a lower price, the SESC said. The fine was much higher than in the other cases. First New York had traded on its own account, while in the other cases, funds were investing on behalf of other investors, subjecting them to lesser penalties under the SESC's rules.

The SESC said a sales staff member at the underwriter passed on word of the Tokyo Electric share offering to a trader at First New York via a director of a consulting firm which it did not identify. The director also took out a short position, the SESC said, and was fined 60,000 yen.

On that day Nomura for the first time publicly acknowledged that its employees were the sources of leaked information in the three cases brought so far - Tokyo Electric, Mizuho and Inpex. ($1 = 78.7300 Japanese yen)

(Reporting by Nathan Layne; Editing by Ian Geoghegan)