The key witness in one of the several cases against Israeli Prime Minster Ehud Olmert, American businessman Morris Talansky, has declared that he won’t be returning to Israel in order to complete his testimony.

Olmert’s people say this shows how unreliable a witness he is – and leaves the prosecution’s case in tatters. The prosecution retorts that its case is still strong, and that Olmert will still be indicted.

And I hope the prosecution is right.

Why? After all, having a former Prime Minister in the dock – and convicted – will be a major embarrassment and a tragedy, particularly in a country in which confidence in the political system has reached an all-time low.

But I worry that having the prosecution’s case fail would be even worse.

Although there have, recently, been a couple of convictions of minor MKs – Naomi Blumenthal and Haim Ramon – Israeli police have now gone after quite a string of very senior politicians with very few cases ever coming to court, let alone ending with a guilty verdict.

Serious corruption investigations which went nowhere were launched against, amongst others, former PMs Ehud Barak, Benjamin Netanyahu and Ariel Sharon.  None of them were ever charged with any wrongdoing, but the cases seriously damaged their reputations and hampered their ability to function in the political arena.

Meanwhile, Ariel Sharon fired minister Joseph Paritzky in 2004 after he was accused of attempting to incriminate a political rival – but the case was closed for lack of evidence in 2005. The Attorney General this week decided to close a corruption file against Tourism Minister Ruchama Avraham which goes back to 2004, due to lack of evidence. Similarly, he dropped one of his criminal investigations against former minister Avigdor Lieberman this week, although he will continue several others; the file against MK Lieberman goes back at least as far as 2001, so far with no charges. The trial of former environment minister Tsachi Hanegbi, for handing out government jobs to his political allies, has been dragging on since 2005. Only the embezzlement case against former finance minister Avraham Hirschson, for theft and fraud, actually seems to be moving.

All these dead-ends are bad enough. But this time round, the prosecutors have actually forced the resignation of a prime minister. This is an extremely serious result, which cannot be taken lightly. Should it emerge that the prosecution’s case was built on sand; or that they cannot carry the case through because their main witness won’t appear – this will truly devastate confidence in the police and the legal system, which many already suspect of deliberately targeting certain politicians for political reasons.

Clearly, I would not want Olmert to be convicted of anything of which he is not actually guilty. But for the law enforcement authorities to emerge once again as destabilising and distorting Israel’s politics on a flimsy basis would be a true blow to the rule of law, from which the country would find it hard to recover.