The Pakistan cricket match is normally fixed in the following way.
A couple of weeks before a match the bookie goes to one of the politicians in the government and offers a price. The politician then consults the PCB Chairman who then in association with the captain and the players fix a certain price (this price is normally around £50,000 - £100,000 per person). The politican then agrees the price with the bookie and hence the match is fixed.
What the pakistani team normally do is that certain players agree to perform below par. Hence in a fixed match some players will be seen fighting hard and some will look very casual. The team will normally start very poorly and towards the end will fight extremely hard, but still wil loose the match. The advantage of this strategy is that captain can say in the end that we fought hard but were unlucky.
What I presume happened in the world cup is that Pakistan fixed the first match against W.I. The bookie offered a very high price to book the second match too but PCB and players refused. But due to a green track and Ireland performing brilliantly the team ulimately lost. Bob woolmer who was against the idea of fixing the first game was furious and was about to speak out. The players who were scared of their reputation told the bookie's sources. The bookie decided to killed Woolmer.
It may sound a little filmy but that has been the history of Pakistan Cricket. Even if the captain doesnt want to fix a game, the PCB and the government forces are so strong that he and the team has no option.