Image copyright Getty Images Image caption There has been a series of murders of bloggers and activists in recent months

Two criminal cases have been filed in Bangladesh against three men arrested for hacking to death a Hindu tailor.

The murder of Nikhil Joarder by suspected Islamist militants on Saturday was the latest in a wave of murders over the past three years.

More than 20 people, including bloggers, academics, foreigners and religious minorities, have been killed.

So-called Islamic State said it carried out the attack, accusing the dead man of insulting the Prophet Muhammad.

However the authorities deny the group is active in the country.

Nikhil Joarder spent two weeks in prison in 2012 for allegedly insulting the Prophet but the complaint was withdrawn.

The BDNews24 news agency has reported that two cases had been initiated in connection with the murder - one by the victim's family and another by local police over the discovery of small bombs allegedly found in a bag left at the scene of the crime by the assailants.

Police in the central district of Tangail say that among those they have detained over the murder is the principal of a madrassa or Islamic religious school.

Image copyright AP Image caption The government has denied accusations that it is not doing enough to stop the killings

Image copyright AFP Image caption The murders have led to demonstrations denouncing the killers across Bangladesh throughout April

A local official of the country's largest Islamic party, the Jamaat-e-Islami, is also being questioned, along with a member of the main opposition Bangladesh Nationalist Party.

Mr Joarder was hacked to death while sitting outside his shop by assailants who escaped on a motorbike.

His killing came just a week after leading gay rights activist Xulhaz Mannan and his friend were brutally murdered in the capital Dhaka.

Image copyright AP Image caption The murder overshadowed Labour Day celebrations on Sunday

A Bangladeshi militant group affiliated to al-Qaeda, Ansar al-Islam, said it was behind those killings.

The government has blamed all the attacks on opposition parties or local Islamist groups. It has been strongly criticised for not being able to prevent the violence or bring suspects to justice. Opposition parties deny the claims.

In a speech to mark Labour Day on Sunday, Prime Minister Sheikh Hasina said it was members or supporters of her party who were mostly being targeted by the killers.

Last year, four prominent secular bloggers were killed with machetes.

The four bloggers had all appeared on a list of 84 "atheist bloggers" drawn up by Islamist groups in 2013 and widely circulated.

Who exactly is behind the attacks remains murky. Bangladesh has myriad extremist groups and there have been few convictions over the attacks.