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Dan White: The arrest of Seanie -- why it happened and what it means for the rest of us ...

The arrest of former Anglo Irish boss Sean FitzPatrick has caused consternation in Dublin's financial circles.

But what does it all mean? Here, we deal with some of the tough questions that need to asked about the affair.

Over a 22-year period, first as chief executive and from 2004 as chairman, FitzPatrick presided over the exponential growth of Anglo Irish Bank.

By 2007, what had been a tiny lender 21 years earlier was Ireland's third-largest bank with a total loan book of €72bn and a market value of €13bn.

As the property bubble has turned to bust, Anglo has been revealed to be a house of cards. The state has already pumped €4bn of fresh capital into Anglo and the Central Bank has lent it a further €10bn.

The State had to nationalise Anglo in January 2009 to prevent it going bust.

Probably, but Anglo is by far the worst case.

It is now clear FitzPatrick's management of the bank was utterly irresponsible. Anglo has already written off €4bn of bad loans.

It is expected to reveal a further €14bn of loan losses when it reports its results in a few weeks' time. With €32bn, almost half of its total loan book, going to NAMA it is now clear FitzPatrick has serious questions to answer about his management of Anglo.

Unfortunately, things were even worse at Anglo. FitzPatrick was forced to quit as chairman in December 2008, when it emerged that he had concealed personal loans from Anglo, which had at one stage exceeded €120m, from shareholders and regulators for eight years.

Concealing loans to directors is a serious no-no for any bank. It goes to the heart of its credibility with depositors and investors.

As if this weren't bad enough, it is now clear that FitzPatrick roped in another financial institution, Irish Nationwide, to help him conceal these personal loans.

No. In September 2008, in the days coming up to its financial year end, Anglo deposited €7.4bn with IL&P, which in turn routed the money back to Anglo.

However, instead of categorising this money as an inter-bank loan, it was described in the Anglo accounts as a customer deposit.

This made Anglo's financial situation appear much less desperate than it actually was, deceiving regulators, shareholders and investors.

Yes there is. From late 2007, Sean Quinn, one of Anglo's largest customers, accumulated a stake of more than 25pc in the bank. He managed to avoid having to disclose this shareholding to the Stock Exchange by purchasing financial derivatives, known as contracts for difference, rather than ordinary shares.

When, in the summer of 2008, Quinn offloaded a 10pc Anglo shareholding, the bank lent ten of its other main customers €451m to buy them.

As most of these loans were non-recourse, i.e. secured only on the shares which are now worthless, Anglo has had to write off €310m on this transaction alone.

Unfortunately, former Financial Regulator Paddy Neary, who retired in January 2009, seems to have gone AWOL.

He apparently knew about the concealed loans for 11 months but failed to act on that information.

Very good question. Unlike AIB, Bank of Ireland or IL&P, which have large numbers of current accounts, personal loans and mortgages on their books, Anglo was always a niche bank. If it had been allowed to go bust in September 2008, it would have saved the taxpayer a fortune.

With total loan losses already heading for €18bn, a quarter of its total loan book, it is clear that there will be little if any change out of €20bn by the time the taxpayer has picked up the full tab for Anglo.

If they haven't already done so, gardai will want to talk to someone from IL&P or Irish Nationwide.