Help the prisoners, when did the gas bombs drop?

Question

A prison has a mathematician. It was Sunday. The warden tells the parishioner that a nearby army plans to gas the prison during the next week. And that he was told to tell the mathematician that he would not know the day. There was a bunker, where the mathematician and his cohorts could hide from the gas for 24 hours and no more. The warden and the guards had gas masks for themselves. What did the parishioners do?

This is a sort'a follow up to this problem: http://answers.yahoo.com/question/index;_ylt=AhylJO15TN50EYJc17sp_uzty6IX;_ylv=3?qid=20080828133144AA7jtO3&show=7#profile-info-d3339228e63a53e480f5bb320ea841cfaa

Answer 1

They should do nothing.  The reason is straightfoward:  If the last day they're going to be gassed is the following Sunday, then by Saturday the prisoners would know when they'll be gassed, so that the would know the day.  Then that means on Friday, since they know that by Saturday they'd know the day, they'd know that it cannot happen on Saturday, since that would be expected.  And so on, all the way to Monday.  That is the logical conclusion.  Of course, they will all be gassed on a Sunday, but at least the prisoners knew that they wouldn't be gassed on that Sunday.  

Answer 2

1) The parishioners were at  the Sunday church service.

After hearing the bad news:

2) The parishioners left the parish near as fast as light.

Answer 3

This seems like the hangman/unexpected-death paradox, but misquoted.

As the question states it, I don't think anything can be done logically to determine the day (even fallaciously, like some "solutions" to the hangman paradox do).

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Continuing the story after scythian's answer:

Then they're gassed on Thursday, catching the mathematician entirely by surprise.