The theory that Megrahi was responsible is still held to be true by the governments of Scotland, the UK and the USA, and he was convicted by a court, so we have to bear that in mind. However...

The journalist Paul Foot, in conjunction with the UK magazine Private Eye, set out a very convincing case for the bombing having been ordered by Iran as revenge for the destruction of one of its airliners in an accidental shooting down by the USS Vincennes. Private Eye produced a special edition of the magazine setting out all of Foot's investigations - I would imagine that you can find a copy on eBay (I have one myself somewhere). In 2011, Aljazeera produced a pair of documentaries on the subject which essentially presented Foot's research to a TV audience - you can find the documentaries online here - http://www.aljazeera.com/programmes/lockerbie/2014/02/lockerbie-what-really-happened-20142247550598601.html

Personally, I believe the evidence against Iran is overwhelming and that Megrahi "took one for the team" to allow Libya's rehabilitation in to the international community.

Edit: Aljazeera documentaries were produced in 2011, not 2014!

This is perhaps not a good subject to ask historians; it's still somewhat of a current event (in that there are ongoing developments and evidence might well be dug up from Libya or elsewhere) and the answers will revolve around not-yet-uncovered conspiracies (whether from Libya, Iran, the PFLP-GC) which tends to lie outwith the field of academic historians; they're more at home when they work with open documentation that they can cite.

There isn't really a satisfactory academic discipline for working with secretive conspiracies of this sort; historians aren't likely to give better answers than journalists - hence why Paul Foot and Al Jazeera and Adam Curtis are the best answers so far.