Prime Minister Manmohan Singh on Thursday wrote a letter to Tamil Nadu Chief Minister J Jayalalithaa saying that an investigation involving a person of the eminence of Kanchi Shankaracharya Jayendra Saraswati -- who is in judicial custody in connection with the Sankararaman murder case -- needs to be conducted with "extreme care and consideration".

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He asked the TN government to "take all such measures as appropriate to ensure the physical well-being" of Jayendra Saraswati.

"I believe that the government of Tamil Nadu has had to take this extreme step of arresting Swamiji keeping in view the gravity of the allegations against His Holiness in the murder case," he said.

"Whereas it is extremely important that due processes of law must not be interfered with and that law must be allowed to take its own course, it is also relevant to note that Swamiji keeps indifferent health.

"His Holiness also enjoys a high religious status and position in society.  The sentiments of individuals are closely associated with His Holiness' well-being."

On two earlier occasions, the PM had said that the Centre had no hand in the seer's arrest.