Bangladeshi counter-terrorism police said on Monday they had arrested a militant wanted for the 2015 killing of a US blogger critical of religious extremism.
The militant, identified as Abu Siddiq Sohel, 34, a member of the al Qaeda-inspired militant group Ansar Ullah Bangla Team, is suspected of taking part in the killing of writer Avijit Roy, deputy police commissioner Masudur Rahman said.
Roy, a US citizen of Bangladeshi origin, was hacked to death by machete-wielding attackers in February 2015 while returning home with his wife from a Dhaka book fair. Roy's widow, Rafida Ahmed, was maimed in the attack.
Sohel, who was identified after analysing CCTV footage, was arrested in the capital Dhaka on Sunday night, Rahman told Reuters.
Bangladesh, a country of 160 million people, is struggling to control attacks by militant groups on secular bloggers, atheists, foreigners and religious minorities.
The most serious recent attack came in July 2016, when gunmen stormed a restaurant in the diplomatic quarter of Dhaka and killed 22 people, most of them foreigners.
Al Qaeda and Islamic State have also claimed responsibility for a series of killings over the past few years, including Roy's.
Authorities have consistently ruled out the presence of such groups, blaming domestic militants instead. However, security experts say the scale and sophistication of the restaurant attack suggested links to a wider network.