A key witness in the investigation into the assassination of Rafik Hariri now claims he was bribed by the slain Lebanese prime minister's family to frame Syria. His claim was dismissed immediately by the Hariri family. But the United Nations probe commission, led by German prosecutor Detlev Mehlis, has confirmed that Hosam Taher Hosam, a Syrian, was indeed one of their witnesses.

The issue raises troubling question even if it is proven beyond reasonable doubt that Hosam is lying. He either lied to the committee as he is claiming now, or he is lying about the whole bribe issue. Whichever is the case, he is a confessed liar. And that fact alone casts a great deal of doubts on the credibility of the Mehlis report, which implicated senior Syrian officials in the assassination of Hariri and upon which hangs the fate of Syria.

Who knows how many other fake testimonies made their way to the report? There could be a number of Hosams. And it is hard to believe the increasingly isolated country is being threatened with severe consequences on the basis of fake testimonies.

Syria was quick to pick up on Hosam's surprising confessions to claim pointers in its efforts to dismiss the report. All along it complained the investigation was politicised and inspired by its "enemies".

It is the responsibility of the UN commission to come clean on that issue. The credibility of its report must be beyond questioning. For unexplained reasons, from the beginning Mehlis dismissed the possibilities of other suspects in the Hariri murder. Against all principles of a proper criminal investigation, he set his eyes on one suspect Syria and has been employing every means to implicate its officials.

The commission needs to reconsider its strategy. It also needs to filter out its witnesses. Its mission must not be exploited by anyone with objectives other than uncovering the truth behind the hideous assassination of Hariri.