This act is an example of SITUATIONAL IRONY,
Situational irony occurs when there is a big difference between what one expects to happen during a situation and what actually happens.
In the passage given above, it can be seen that one will not expect the rioters to start murdering themselves, since they were united against death before, but they abandon their search for death and start murdering themselves; this is a good example of situational irony.
