The 58-year-old was murdered as he walked to the bus station from his home.
The student from Rajshahi University where Siddique taught was arrested early Sunday for questioning, although the hunt was still on for other suspects, said the city’s deputy police commissioner Nahidul Islam.
He said the unidentified student of public administration is a member of Islami Chhatra Shibir, the student wing of Bangladesh’s largest Islamist opposition party the Jamaat-e-Islami.
“We have detained a 21-year-old Rajshahi University student who is a Shibir member as a suspect over the murder,” Islam told AFP, without detailing his alleged role in the attack.
Siddique was the fourth professor from Rajshahi University to be killed by suspected Islamists in recent years.
Five secular bloggers and a publisher have also been murdered, as well as members of minority groups and foreigners, as Bangladesh reels from rising Islamist violence. Police said that in each of the attacks on the bloggers and online activists, attackers hacked the victim to death with machetes or cleavers.
Bangladesh’s counter-terrorism chief Monirul Islam on Sunday rejected the Islamic State’s claim of responsibility for the latest killing, telling reporters that “in reality, the IS does not exist in Bangladesh”.
Other senior police officers made similar statements, echoing the government’s stance that the attacks were carried out by homegrown militants.
“In the past they (IS) issued similar statements on their websites, but we have never found their presence here,” Rajshahi police commissioner Mohammad Shamsuddin told AFP.
Siddique’s wife has said her husband had never spoken out against religion, but police suspect he may have been targeted because he was seen as a free-thinker.
Siddique set up a music school, edited a literary magazine and ran a cultural group that performed music – activities likely to have angered hardline Islamists.
The student group Shibir has a stronghold at Rajshahi University. But thousands of its activists have been detained nationwide in recent years after staging protests against the trials and executions of Jamaat leaders for war crimes committed during Bangladesh’s 1971 battle for independence from Pakistan.
Hundreds of fearful teachers at Rajshahi University boycotted classes and rallied on the campus for a second day on Sunday as they protested against their colleague’s murder. “We seek protection of all teachers. We’re all feeling insecure,” said university
“If a harmless and innocent person like Professor Siddique can be murdered, nobody is safe. We want the immediate arrest of the killers,” he said. A long-running political crisis in Bangladesh, which is majority Sunni Muslim but officially secular, has radicalised opponents of the government and analysts say Islamist extremists pose a growing danger.