Shafiur Rahman Farabi, who had issued repeated death threats to writer-blogger Avijit Roy, was arrested by the Rab in the capital's Jatrabari area early yesterday.

Known in the social media and blogsphere for his vitriolic campaigns against progressive and free-thinking bloggers, Farabi is the key suspect in the Avijit murder, the elite-crime buster said.

Avijit's father too alleged that Farabi had been threatening his son for the last one and a half years, said Rab officials.

A Rab team arrested the 29-year-old around 5:30am at Jatrabari Bus Terminal when he was about to leave for Chittagong, said Mufti Mahmud Khan, director of Rab's legal and media wing, at a briefing later in the day.

He was detained twice before - in 2010 for vandalism on Chittagong University campus and in 2013 for issuing death threat to the imam who conducted namaz-e-janaza of Rajib Haider, a blogger chopped to

death in Mirpur on February 15 the same year.

He was indicted under the ICT act following his arrest on February 24, 2013. But he came out on bail after about six months and started to incite killing of free-thinking bloggers.

Farabi again came to the fore

after Avijit was hacked to death and his wife Rafida Ahmed Bonya seriously injured on Dhaka University campus on Thursday night.

During a preliminary interrogation, he denied his involvement in the murder but said he supports it and that Avijit got "what he deserved”, a Rab official said, wishing not to be named.

The detainee was handed over to the Detective Branch (DB) of police, which is investigating the murder case.

"The information we have gathered so far suggests Farabi might have link to the killing," said Rab official Mufti.

Farabi had first come in contact with Avijit, founder of Mukto-Mona blog site, four to five years ago on Facebook, Mufti quoted the detainee assaying.

The two soon got locked into feuds. Farabi started using SMS for threatening Avijit after the writer stopped communication with him.

The Rab also said in a statement that a Facebook friend sent Farabi a photo of bloodied Avijit after

Thursday night's attack and asked, "Have you got the pictures?" He replied he got those.

As the friend wanted to know his reaction, he said he would be arrested anytime soon.

"Such matters suggest Farabi was directly linked to the killing,” said the Rab statement.

Meanwhile, the Rapid Action Battalion marked five persons in video clips of close-circuit cameras installed in Dhaka University area for Amar Ekushey Book Fair. One of them was seen pointing to Avijit.

Their identities, however, could not be known yet as the images were not clear, Mufti said.

Yesterday, family members, who met Bonya at the Square Hospital, said she was improving. Despite her serious injuries, she remains adamant that she will do whatever it takes to get justice for the killing of her husband.

Being an American citizen, she will contact US investigators for tracking down the killers, they quoted her as saying.