The one victim named in the article appears to be from the Hindu community - about 8% of the total population. If the others are also Hindu (or from anywhere outside of the majority Sunni Muslim population) then this is just part of the ongoing oppression suffered by all religious minorities in Bangladesh.
If the pretext for such action wasn't witchcraft, then blasphemy would serve. And it's not really necessary to be backward-looking and superstitious - this is about politics first and foremost. It's the way most Muslim states purge, or otherwise cow, their 'non-believers' - take a look at the demographics of Muslim states, how do you think they manage to be so disproportionate? As we in the West become more diverse, they become less so.
Bangladesh is relatively diverse by Muslim standards at only 88% Sunni Muslim and 2% Shia - but not for much longer.