The Mumbai Police Crime Branch today handed over one of the five it had detained for questioning last week to the Anti-Terrorist Squad (ATS) after it found ‘‘substantial evidence’’ of his involvement in Terrible Tuesday’s serial train blasts.

The accused has been identified as Dr Tanvir Ahmed Mohammed Ibrahim Ansari (33), a practitioner of Unani medicine and resident of Byculla. Ansari was arrested later in the day by the ATS and produced before a magistrate who remanded him in police custody till August 4.

Sources said Dr Ansari — fourth person to be arrested in the 7/11 serial blasts case — was part of an ‘‘extremely sophisticated and dangerous’’ LeT module that may be connected with the October 29, 2005 Sarojini Nagar market blasts in Delhi that killed over 40 persons, and the June 3, 2001 blast at a Roman Catholic church in Gopalganj, Bihar, in which 10 persons were killed. ‘‘However, his (Ansari’s) role in the recent blasts in the city is being investigated,’’ said a senior Crime Branch official on conditions of anonymity.

According to ATS officials, investigating the serial train blasts, Ansari is part of a module of five persons in the city, who have all been trained in Pakistan. Investigations till now have revealed that Ansari had gone to Pakistan by road from Tehran, where he had gone on a pilgrimage visa, in late 2004.

Officials said the modus operandi of visiting Pakistan through Iran was similar to the one employed by members of the Lashkar’s Aurangabad module and the one busted in Delhi on May 9.

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