ASM Ashraful Islam, labour counsellor at the Bangladesh embassy in Libya, told bdnews24.com from Tunisia on Tuesday that two boats started for Italy at the same time on the night of May 9.
The first one carrying about 50 might have reached Italy but the second one with around 70 on board capsized, according to him.
As many as 14 Bangladeshi nationals were rescued alive from the capsized boat, he said.
The rescuers also found the body of Uttam Kumar from Naria in Shariatpur, according to the official.
“The rest 40 to 45 Bangladeshi nationals are still missing. Chances of getting any more bodies are nearly impossible," Ashraful said.
Red Crescent official Sayeda Abida Farhin had said there are fears that the number of Bangladeshi casualties may be more than anticipated.
The disaster struck after the migrants had set sail for Italy from the conflict-ridden Libya.
The overcrowded vessel subsequently sank in the Mediterranean Sea off the coast of Tunisia on Friday, killing at least 65 people, the majority of whom were Bangladeshis.
A total of 16 people were rescued by Tunisian fishermen and 14 of them were Bangladeshis.
On Sunday, Foreign Minister AK Abdul Momen told reporters that 30 to 35 Bangladeshi were feared dead in the accident.
But Farhin said quoting Tunisia's Red Crescent that there were 85 to 90 passengers on board the vessel. Of them, 32 were Egyptian nationals, according to some survivors.
"It's being presumed that there may have been 50 to 55 Bangladeshi passengers on the boat. In that case, the number of Bangladeshi casualties may be more than previously thought," she said.