The arrest yesterday of Libya's former spy chief Abdullah al-Senussi could at last shed some much-needed light on the Lockerbie atrocity.

If anyone knows the details of Libya's involvement – or non- involvement – in that terrible mass murder, it is Senussi.

As our sister paper The Herald made clear in reports last week, there remain serious doubts over the guilty verdict delivered on Abdelbaset Mohmed Ali al-Megrahi.

The Scottish Criminal Cases Review Commission has suggested that, among other flaws in the court case, evidence important to the defence was kept from Megrahi's lawyers.

There are doubts too over the circumstances surrounding Megrahi's eventual release on compassionate grounds to allow him to return home ''to die''.

We have heard suspicions that Westminster politicians were acting behind the scenes to encourage the release. And there has been a strenuously denied claim that Holyrood Justice secretary Kenny MacAskill had suggested Megrahi's chances of release would be greatly boosted if he were to drop his appeal.

It is unfortunate, to say the least, that the appeal was dropped. The best place to test Megrahi's conviction would have been in court. For reasons that remain unclear, the appeal looks unlikely to be revived.

The vacuum around the case has acted as a breeding ground for countless conspiracy theories.

If Senussi holds the key to unlocking some of the Lockerbie mysteries, we need to discover what he knows.