I found this about Moonlight Shadow on this interesting enough looking site:

4.2 Is Moonlight Shadow about the murder of John Lennon?

Maybe Mike was influenced by the murder of John Lennon, which might have found a way into the song, but it was not specifically written about it. Mike himself said he doesn't know exactly, it should be taken without a deep meaning. When Mike was interviewed for the mailing list (see http://tubular.net/articles/95_06.html), this question was asked too. He replied that the song was originally inspired by a very old film called 'Houdini', a Paramount picture filmed in 1953, directed by George Marshall with Tony Curtis in the title role. Additional information is available from:
http://uk.imdb.com/M/title-exact?Houdini%20%281953% 29.

Myself, I remember at the time I took it as being maybe related to the Troubles in Northern Ireland.