By Subir Bhaumik
BBC News, Calcutta
Intelligence agents fear Mukhtar Ahmed's family is at risk
Questions have been raised in India over the police handling of the arrest of a man suspected of handling mobile phone cards used by Mumbai's attackers.
Calcutta police arrested Mukhtar Ahmed for procuring SIM cards for the group without knowing that he was an undercover operative.
He was on a long-term mission with police in Indian-administered Kashmir.
Senior intelligence sources say a "high-value asset" has been blown and his family put at risk.
Mukhtar Ahmed has told those questioning him that he was working for police intelligence in Indian-administered Kashmir.
His brief was to procure SIM cards for Lashkar-e-Taiba fighters and pass the numbers to police so that all calls from those numbers could be monitored by intelligence.
Calcutta police officials admit that Mr Mukhtar has given them details of his work but say they can release him only if police in Indian-administered Kashmir make a formal request in writing.
Police there may be reluctant to do so as intelligence operatives rarely own up to undercover operations publicly.
Mr Mukhtar's identity is now in the public domain and police in Indian-administered Kashmir are neither owning up to his work nor disowning him.
The senior federal Intelligence Bureau official said: "This exposure will put Mukhtar and his family at great risk.
"Why should the Calcutta police leak his name to the press when we had told them categorically to keep shut on the entire Mumbai investigations?
"They thought they had a huge catch and they wanted publicity."
He said Calcutta police should have checked with Indian-administered Kashmir police once they arrested Mr Mukhtar.
"A high-value asset has been blown, a major operation has been screwed up," said the Intelligence Bureau official.
He said a SIM card recovered from the mobile of one of the Mumbai gunmen, called Ismail, was among those supplied to Lashkar by Mukhtar Ahmed.
"But it was only switched on once before the attack and hardly used because Ismail got into action and was killed by police soon after," the official said.
Mr Mukhtar and Tousif Ahmed, the Calcutta trader who procured the SIM cards for him, may be handed over to Mumbai police because they are wanted in connection with the attack.