The case reached the high court through Nasir's relative, Suman Molla, but the bench found multiple inconsistencies in the claims made on his behalf.
Suman told the court that Nasir's father had died in 1980 and that he had brought him up. The bench, however, said it was inclined to "disbelieve" the claim because official records showed Nasir was 46 years old while Suman was only 38.
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The judges also observed that Nasir and Suman had not approached the court with "clean hands". While Suman had identified himself as Nasir's cousin during police questioning, he later claimed before the court that he was Nasir's uncle.
During the hearing, the court allowed Suman's lawyer to speak to Nasir, who is being held at the Lalgola detention centre, to ascertain the whereabouts of Nasir's mother.
Nasir said both his parents had died and were buried but could not identify the burial site. The bench observed that a DNA test could have been conducted to verify his claim if he had been able to specify the location of the graves.
On the first day of the hearing, the state's counsel informed the court that Nasir had admitted while in detention that he was a Bangladeshi national who had entered India illegally several years ago.
The bench chose not to rule on whether such an admission, made while in detention, should carry the same legal effect as one made while in police custody.
"Even if we are to apply the principle that an admission made in the custody of the police should be discarded, nonetheless, the onus of establishing citizenship remains with the detainee," the bench held.
Nasir could not produce a birth certificate. On his behalf, Suman submitted a voter ID card, Aadhaar card, PAN card and a United Bank of India passbook.
The court said these documents, by themselves, were insufficient to establish citizenship.
"A voter identity card is not conclusive proof of Indian citizenship. It is evidence of the detainee's enrolment on electoral rolls," the bench said, noting that Nasir's name had been deleted from the electoral roll during the Special Intensive Revision (SIR) process.
"Aadhaar, too, cannot by itself be conclusive proof of Indian citizenship," the court said, adding that the same observation applied to a PAN card and a bank account.