DHAKA: The father of an American writer slain last month in his native Bangladesh has accused police of negligence in the crime and said officers allowed the attackers to escape.

In comments on Saturday to Bangladeshi media, Ajay Roy said he was “not satisfied” with the investigation of the killing of his son, Avijit Roy, who was attacked by a group of men wielding machetes outside Dhaka University in the capital.

Avijit Roy’s widow, Rafida Ahmed Bonya, was wounded in the Feb. 26 attack just a few yards from Shahbagh Police Station. She said police officers stood by like spectators and watched the attackers flee.

A top government official also criticised the police response and called on the police chief to “identify the black sheep” within the force and bring them to justice.

“It is unacceptable that the murder of Avijit took place right in front of the nose of police,” H.T. Imam, political adviser to Prime Minister Sheik Hasina Wajed, told an audience at the university.

Roy, an outspoken critic of extremists who had received death threats, was visiting Dhaka from his home in the Atlanta area. Imam said Roy was killed because the 2004 death of another prominent secular writer, Humayun Azad, went unpunished.

“Policemen who are not helping people, I think they are the black sheep of the service,” Imam said. “Find and punish them. Then people’s faith in police will return.” Violation of human rights will also stop, he said.

Bonya, an American citizen, is recovering from head injuries, and one of her thumbs was sliced off. Now back in the United States, she said in a statement that the family “demands that the Bangladeshi government do everything in its power to bring the murderers to justice.”

FBI agents were in Dhaka assisting in the investigation.

A court ordered that a suspect being held since March 3, Shafiur Rahman Farabi, remain in custody for another five days.

Farabi, described by police as an Islamic “fundamentalist blogger,” had made death threats against Roy on social media but denied taking part in the attack.