Four trains are currently stranded at both ends of the Bangabandhu Bridge
Police say they suspect extremists were behind the killing.
Dhaka Metropolitan Police’s Joint Commissioner Monirul Islam on Sunday said the FBI, too, thought it was the work of religious fanatics.
US citizen Avijit, an Atlanta-based bioengineer by profession, and his blogger wife Rafida Ahmed Bonya were attacked on the Dhaka University campus on Feb 26.
The FBI is assisting Bangladesh investigators.
Avijit had received threats for his secular writings. Bonya, who lost a thumb and was seriously wounded in the attack, has flown back to US for treatment.
Islam said they had a list of people who had threatened or encouraged the killing on social media.