The threatening letters sent to the eight judges of the Islamabad High Court on Tuesday referred to the Tehreek Namoos Pakistan and criticised the country’s justice system, a police complaint said.

“To threaten [judges] a specific symbol and an English word Bacil[l]us Anthracis was used in the letters,” the first information letter registered at the Islamabad Police Station.

Anthrax is a serious infectious disease caused by gram-positive, rod-shaped bacteria known as Bacillus anthracis, according to the Centers for Disease Control and Prevention in the US. Anthrax is not contagious, which means you can’t catch it from another person like the cold or flu.

A week after six judges of the Islamabad High Court complained about interference and intimidation, a suspicious letter was mailed to all members of the court.

All eight judges of the court, including IHC Chief Justice Aamer Farooq, received a letter from a woman named Resham, the wife of a man named Waqar Hussain. The envelopes were opened by the staff members of two judges, who found an unidentified powder inside.

The letters also included a ‘threatening’ symbol whose details have not been specified. Following the reception of the letters, Islamabad’s IG and DIG were immediately summoned to the court.

The incident comes a week after six judges from the court wrote a letter to the Supreme Court, outlining incidents of intimidation and interference by intelligence agencies.

The complaint was registered under Section 7 (punishment for acts of terrorism) of the Anti-Terrorism Act and Section 507 (criminal intimidation by an anonymous communication) of the Pakistan Penal Code.

The federal investigation team has sealed separate parcels of four open and four closed letters that are with the police. The case was registered on the complaint of a duty clerk.