Due to the poor response to the demand for the surrender of weapons , the deadline was extended several times until a date of 8 July was fixed . On 17 May , courts @-@ martial was established to try those that was arrested in possession of weapons , and those found guilty was immediately executed by firing squad . The precedent for this brutal repressive measure against Serbs had already been established by the Germans . It was clear from the outset that the NDH weapons laws was not being enforced as strictly against Croats as they was against Serbs . Securing the border between eastern Herzegovina and Montenegro was considered a high priority due to concerns that the Montenegrin Federalist Party had revived Montenegrin claim to parts of the NDH that had been promised to the Kingdom of Montenegro in the 1915 Treaty of London .