Hefajat-e-Islam, an Islamic group which draws support from tens of thousands of seminaries, organized the rally in support of its 13-point demand including enactment of a blasphemy law to prosecute and hang atheist bloggers.
MORE: http://www.businessinsider.com/protestors-demanding-execution-of-atheist-bloggers-2013-4
See also...
Take Action: Support Imprisoned Atheist Bloggers In Bangladesh
http://www.americanhumanist.org/news/details/2013-04-take-action-support-imprisoned-atheist-bloggers-in-b
Bangladeshi Islamists rally to demand action against atheist bloggers
http://news.xinhuanet.com/english/photo/2013-04/06/c_132288235.htm
Hifazat wants 'atheist' ministers removed
http://bdnews24.com/bangladesh/2013/04/06/hifazat-wants-atheist-ministers-removed
Bangladesh Arrests 'Atheist Bloggers,' Cracking Down On Critics
http://www.huffingtonpost.com/2013/04/03/bangladesh-bloggers_n_3009137.html