This is my 'A' post for Crime Fiction Alphabet 2012.
Alibi is defined a claim or piece of evidence that one was elsewhere when an act, typically a criminal one, is alleged to have taken place: she has an alibi for the whole of yesterday evening . Oxford English Dictionary
If you have an alibi it is bad because
"...because only a man with a criminal enterprise desires to establish an alibi." as Sherlock Holmes points out to Watson.
If you don't have an alibi, and were at home alone it is worse because
Home Alone was a movie, not an alibi.
~ Jerry Orbach
It is important as G K Chesterton points out in The Ghost of Gideon Wise
the theory by which it is maintained, in defiance of the mythological Irish bird, that it is impossible for anybody to be in two places at once.
Criminals go to great extents to establish Alibi in fiction. They use actors to act as double while they commit the murder. They use an accomplice. Or invent or use devices that would kill while they are out establishing their alibi. Add just one poisonous pill to a bottle full of daily medicines. Friends and loved ones are always helpful, if you need one, they provide you one with.
"The nature of alibis has not changed much in two centuries." The Franchise Affair, Josephine Tey
The most common Alibi is watching a movie in a Cinema and show the ticket stub as a proof. Wonder how many people do take back tickets home to keep it, just in case one needs an Alibi. The other most common alibi that people don't readily admit to but always bring it up at the last moment - being unfaithful to their spouse.
A is for Alibi is also the first book in the Kinsey Millhone Alphabet series by Sue Grafton. As far as I remember this book got nothing to do with Alibi. But a decent mystery. All her other books are great.
Finally from my love-hate poet T. S. Eliot's Macavity: The Mystery Cat
He always had an alibi, and one or two to spare:
At whatever time the deed took place -
Macavity wasn't there!