The deceased writer's namaj-e-janaza was held in Lalmatia after Isha prayers.
Earlier, the body of Mushtaq was handed over to his family at 12:30pm following completion of an autopsy.
The writer was arrested last May in a case filed under the Digital Security Act and charged with spreading disinformation against the government on social media.
He suffered a heart attack inside his cell at the high-security Kashimpur prison on Thursday evening, it was learnt.
Mushtaq was transported to Shaheed Tajuddin Medical College Hospital, but declared dead on arrival, Senior Jail Superintendent Md Gias Uddin said.
Also read: Writer Mushtaq, arrested under DSA, dies in custody
"No apparent injury marks or other symptoms were found on his body during the autopsy. However, the cause of his death can be confirmed after conducting detailed examinations," Dr Safi Mohaimen, head of the forensic department of Tajuddin Medical College, said.
Syed Bayezid, sub-inspector of Sadar police station under Gazipur Metropolitan Police, said, "Sores were found on his right hand and back. The wounds may have occurred when his body was transported to the hospital in the ambulance. However, it can be confirmed after receiving the autopsy report."
Hundreds of students, teachers, and civil society members offer a ghaibana namaz-e-janaza (funeral prayers in absentia) for writer Mushtaq in front of the National Museum in Shahbagh. Photo: UNB
An unnatural death case has been filed with Gazipur Metropolitan Police's Sadar Police Station over Mushtaq's death in custody, Bayezid added.
Mushtaq's brother Dr Nafisur Rahman, who was waiting at the hospital morgue, stated: "I saw the body myself and did not notice anything unusual. An autopsy has been completed. What else can I say without having the autopsy report?"
The 53-year-old writer, who published the book "Kumir Chaasher Diary" under the pen name Michael Kumir Thakur, was picked up by Rapid Action Battalion (RAB) from his Lalmatia home on May 2, allegedly for posts critical of the government's handling of the Covid-19 pandemic.
Also read: Writer Mushtaq's body handed over to family after autopsy
On August 20, he was shifted to the Kashimpur prison, Gias Uddin said.
Calls for Mushtaq's release were widespread and sustained throughout his time in prison. Soon after his arrest, more than 300 dignitaries in Bangladesh issued a joint statement demanding his release, alongside cartoonist Ahmed Kishore.
However, his bail applications were turned down on at least four occasions.
Amnesty International reiterated the demand in a statement as recently as January, saying the duo (Kishore and Mushtaq) had been arrested "solely for the peaceful exercise of their right to freedom of expression."
Mushtaq's death triggers protest
Meanwhile, hundreds of students, teachers, and civil society members offered a ghaibana namaz-e-janaza (funeral prayers in absentia) for writer Mushtaq on Friday in front of the National Museum in Shahbagh.
Progressive Students’ Alliance brings out a procession from TSC area around 11am, parades Shahbagh and Paribagh, and later blocks the Shahbagh intersection. (UNB photo)
However, police baton-charged the left-leaning organisation members who were demonstrating at TSC of Dhaka University this evening, over the death of Mushtaq.
Also read: Writer Mushtaq's death in custody triggers protests
The incident took place when the protesters brought out a torchlight procession in the area around 7pm.
Police obstructed them and detained some of the protesters from the spot, leading to a clash between the two sides.
At one stage, police fired teargas, forcing the protesters to take up positions in front of the central mosque of Dhaka University. At least 20 protesters were reportedly injured in the clash.
OECD envoys appalled by Mushtaq's death in custody
Thirteen Ambassadors and High Commissioners stationed in Dhaka on Friday urged the government of Bangladesh to conduct a "swift, transparent, and independent inquiry" into the full circumstances of writer Mushtaq's death in police custody.
The diplomats of the Organisation for Economic Co-operation and Development (OECD) member countries with missions in Bangladesh made the call in a joint statement expressing their grave concerns over the death.
Also read: OECD envoys appalled by Mushtaq's death in custody; demand inquiry, answers
"The undersigned heads of mission in Dhaka express our grave concern about the death in custody of Mushtaq Ahmed on 25 February 2021," reads the joint statement.
"We understand that he had been denied bail on several occasions and that concerns had been raised about his treatment while he was imprisoned," the statement said.
Also, the diplomats expressed their sincere condolences to his family and friends.
"We will continue to engage with the government of Bangladesh on our governments' wider concerns about the provisions and implementation of the Digital Security Act, as well as questions about its compatibility with Bangladesh's obligations under international human rights laws and standards," they said.
Also read: 'The government is Mushtaq's murderer': Nur
Digital Security Act
Mushtaq Ahmed may go down as the first victim of the dreaded Digital Security Act to have paid with his life. Adopted by a rubber stamp parliament in October 2018, ostensibly to replace the flawed ICT Act of 2006, it has proved to be a monster in the books, subject to wanton misuse and capable of being weaponised for abuse. Well before it was passed into law, discerning observers sounded the alarm almost as soon as the draft of the proposed legislation was published.
Throughout 2018, in a series of public hearings prior to enactment, citizens raised objections to different portions of the then-proposed bill. Representatives of the executive branch would provide assurances of addressing their grievances, of amending the language, or not invoking its most troubling bits.
For example in May 2018, journalists sat with a parliamentary standing committee on the ICT Ministry and aired specific grievances against 8 separate sections of the bill placed before them. Law Minister Anisul Haque and ICT Minister Mostafa Jabbar attended the meeting on special invitations.
At the end of the meeting, members of the committee assured the journalists that the relevant portions would be 'fixed' before it passed into law.
Jabbar was quoted as saying: "We are in agreement with the journalists about amending the sections they have problems with. We are going to bring necessary amendments so the freedom of press does not get hampered.”
Yet none of the amendments were ever made, and nothing was 'fixed' prior to its passage in parliament by voice-vote, effectively making a mockery of the meeting with journalists, and casting aspersions on the government's motives for bringing in such a law.
In the 28 months since, this country has seen enough, and more, to know the answer to that. Law enforcement agencies, government officials and ruling party leaders in Bangladesh filed 80% of all Digital Security Act (DSA) cases in 2020, according to UK-based free speech advocates Article 19.
A total 198 DSA cases were filed in 2020, as compared to just 63 in 2019.
Among the DSA cases filed last year, 99 cases were filed over defamation or criticism of the prime minister, MPs, or local administrators, 17 filed for hurting religious sentiment and 13 for spreading rumours about Covid-19.
The data shows a spike in cases in the first few months of the Covid-19 outbreak, with a drop-off from August 2020.
The DSA is not just draconian, it is also poorly drafted. Police are given sweeping powers to arrest suspects without a warrant. It abounds with vague and overly broad definitions of offences, at least 14 of which have been made non-bailable.
As 'black laws' go, the DSA is by some distance the blackest of them all. It was perhaps inevitable that sooner rather than later, it would also draw blood. Mushtaq Ahmed turned out to be the unfortunate victim.