Some Jama'atul Mujahideen Bangladesh (JMB) activists recently arrested in Dhaka have blown the lid off these clandestine links during their interrogations, the documents relating to police investigation show.
At least one JMB radical has testified to these links in a judicial confession.
Earlier in January this year, Mazhar Khan, a Pakistani official working in the Dhaka mission, had been expelled after Bangladesh intelligence accused him of funding Islamist radicals and peddling fake currency.
Two of the four JMB radicals, including Idris Sheikh, arrested at Uttara and Khilgaon in Dhaka on Nov 29, were found to be carrying Pakistani passports, said Detective Branch's Joint Commissioner Monirul Islam at a press briefing at the time.
Both these radicals had been travelling frequently between Bangladesh and Pakistan, he said.
Monirul Islam said Idris was in possession of a 'spy mobile', which he was using to communicate regularly with a foreign intelligence agent outside the country.
"He was regularly sharing information with that agent and was also in touch with a female diplomat based in Dhaka." The police officer did not disclose the diplomat's identity at that time.
In his judicial confession before Dhaka Metropolitan Magistrate Abdullah Al Masud under Section 164 of the Code of Criminal Procedure (CrPC), Idris named Second Secretary Fareena Arshad as the diplomat he was in contact with.
The Pakistan High Commission did not respond to bdnews24.com's attempts to cross-check details.
Senior intelligence sources say another junior diplomat of same origin working in a European mission in Dhaka is alleged to have been involved in anti-Bangladesh propaganda.
DB's Monirul Islam told journalists in November that Idris had visited Pakistan via India in 1985.
He married a Pakistani school teacher, Shahnaz Begum, in 1990 and settled in that country. A son, Mohammed Adil, was born.
In 2002, Idris contested national elections from Pakistan Muslim Alliance but lost. In 2007, he returned to Bangladesh and joined the JMB.
Monirul Islam said Idris, 49, had been to Pakistan 48 times in the past two years.
Idris told the magistrate that he had hailed from Chitolmari, Bagerhat and that his father, Kausar Sheikh, was no longer alive.
About his links with Pakistani diplomat Fareena Arshad, Idris said on return to Bangladesh in 2007, he had first tried his hand in garment business, but five years later, he switched over to air ticketing and visa processing.
That is when he first met Babul and then Kamal, who introduced himself as someone working for Pakistan intelligence.
Idris said in the judicial confession that he had run up a huge debt to Babul who had frequently booked tickets for him. Babul, he said, left for Pakistan at one stage and gave him Farina's contact number.
Idris said in his confession that Babul later told him that a man arrested for peddling counterfeit Indian currency in Dhaka airport was closely linked to Farina.
On return from Pakistan, Idris married again – this time Manowara Begum from a neighbouring village. He has two daughters and a son with Manowara.
Government sources said when Idris was arrested at Uttara, he introduced himself as a relative of Prime Minister Sheikh Hasina.
One government source said Idris had earlier been arrested on May 1, 2011 from the house of a top radical.
At that time, he was found carrying 47 passports and a case was filed with the Airport Police.
Idris said in his judicial confession that he got a ride from Farina in her car from Baitul Mukarram to Fakirapool and received Tk 30,000 from her.
An intelligence official told bdnews24.com that Idris had saved a foreign number in his mobile phone as his own.
That number actually belongs to a Pakistani intelligence official called Captain Asim, who is performing a crucial under-cover assignment based in an airport in Pakistan.
The phone Idris carried had the capability to record conversations of other people using malware.