"But what bothers me more is that no one from the Bangladesh govt has reached out to me. It's as if I don't exist."

On a recent evening in a Midwestern U.S. city, a middle-aged woman with bandaged arms and a missing thumb entered a crowded restaurant. Nearby, children coloured with crayons. Waiters rushed by.

The maimed woman, Rafida Ahmed, scanned the room nervously. The Atlanta financial executive has been hiding since religious extremists wielding machetes attacked her on February 26 in Bangladesh.

During the assault, her husband - the Bangladeshi-American blogger Avijit Roy - was hacked to death. Ms. Ahmed sustained four head wounds, and her left thumb was sliced off. On May 3, the Indian-born head of al-Qaeda in the Indian Subcontinent claimed responsibility for a string of attacks in Bangladesh and Pakistan, including Roy's.

In her first extensive interview since the attack, Ms. Ahmed criticised the Bangladeshi government for not responding more aggressively to her husband's slaying.

"This was well-planned, choreographed - a global act of terrorism," she said. "But what almost bothers me more is that no one from the Bangladesh government has reached out to me. It's as if I don't exist, and they are afraid of the extremists. Is Bangladesh going to be the next Pakistan or Afghanistan?"

A spokesman at the Bangladesh Embassy in Washington said he did not know why no one from his government had yet to contact Ms. Ahmed, who, like her late husband, is a dual Bangladeshi-U.S. citizen.

"We are shocked at the killing of Avijit Roy and have taken all measures to find the culprits responsible for this heinous act," said spokesman Shamim Ahmad. "Bangladesh is committed to fighting and ending extremism in all its forms."

The U.S. Federal Bureau of Investigation deployed agents to Dhaka and is working with Bangladesh authorities, an FBI spokeswoman said.

Free thinker

Well known in his native Bangladesh, Roy was largely anonymous in his suburban Atlanta neighbourhood, where the couple lived since 2006.

By day, he worked as a Verizon software engineer. At night, he was a prolific writer, emerging as a leading critic of religious extremism in Bangladesh.

Roy, 43, wrote eight books and moderated a blog called Mukto-Mona (Free Thinker). To some, he was a provocative atheist, but his blog also reflected a strong belief in the value of civil debate, said his stepdaughter, Trisha Ahmed.

"My dad was building a community of secularists who thought rationally," she said. "He wanted to start a conversation and see where it would go."

Roy's activism began around 2000, after he moved to Singapore for graduate school. He moderated a Yahoo email group and the blog followed, said Bangladeshi-British activist Rayan Rashid.

"It was a pioneering group, quite popular, long before Facebook and Twitter," said Mr. Rashid. "He was patient, witty, elegant and mature in dealing with dissidents. His goal was to win them over."

A threat

In 2002, while in Singapore, Roy noticed a blog post from a U.S. woman, who wrote of religion, "I don't understand how people can believe in fairy tales." It was Rafida Ahmed, who would become his wife.

"A lot of people attacked me online for that post," she recalled. "I was a tech manager in Atlanta at the time, a single mom. I was intimidated and didn't respond. The next day, someone named Avijit Roy is defending me."

They dated long distance for years, and he reluctantly moved from Singapore to Atlanta in 2006: Ms. Ahmed would not leave the United States until her daughter completed high school. Roy held a doctorate in biomedical research, but found it easier to get a lucrative job and a U.S. visa as a software architect, his wife said.

After Trisha Ahmed was in college, the couple, by then married and U.S. citizens, decided to visit Dhaka. The two departed in mid-February.

"We knew that anything can happen in a country like that, and we took precautions," Ms. Ahmed said. "There was only one threat against him but we didn't take it seriously. Otherwise, we wouldn't have gone."

Final days

Roy was a star attraction at the book fair. On a tranquil morning before his murder, he outlined a book he planned to write with Ms. Ahmed, and took her on a rickshaw tour of his childhood neighbourhood. He exchanged Facebook messages with his stepdaughter, sharing in her excitement at attending a U.S. college lecture by the feminist Gloria Steinem.

"We were really, really happy," said Ms. Ahmed, who had edited her husband's books in Atlanta, but had not seen his influence first-hand in Bangladesh. "He had finally gotten to show me - in Bangladesh - how and why his work was so important."

Violence against secularists continues. On March 30, a Roy supporter, Washiqur Rahman, was hacked to death hacked in Dhaka by religious extremists.

After Roy's murder, a Dhaka man, who had posted online threats was detained but not charged. Dhaka police have said they believe the Roy and Rahman murders were committed by the militant group Ansarullah Bangla Team.