UPDATE, 22.27 GMT+2. According to posts on Athens IMC, those detained in relation to the Marfin bank deaths have now been released. They have been called to testify again on May 5th.
According to mainstream media reports, police have raided houses in the neighbourhoods of Exarcheia and Kypseli and have detained at least three people, all in relation to the death of the three bank employees in the Marfin bank branch on May 5th, 2010. The same reports indicate that these are all detentions that have not yet become arrests (i.e. the detained have not yet been charged) and that the investigation is ongoing.
More information as it comes.