According to ATS, Ejaz was in touch with terror group Indian Mujahideen's founder Riyaz Bhatkal.
"Sheikh has been remanded in police custody till December 18" by the special Maharashtra Control of Organised Crime Act court, said special public prosecutor Ujjwal Nikam.
Nikam argued in the court that Ejaz was in contact with Riyaz and ATS wanted to interrogate him about Riyaz and the terror module.
According to ATS, Yasin was the key conspirator of the three powerful blasts which took place at Zaveri Bazar, Opera House and Kabutar Khana in Mumbai on July 13, 2011, killing at least 21 people and injuring 141.
Naquee Ahmed, Nadeem Shaikh, Kanwar Pathrija, Haroon Naik and Mohammed Qafeel Ansari are already facing a trial in the case while Riyaz Bhatkal, Waqas Ibrahim Sad, Dubai-based Muzaffar Kolah and Tehseen Akhtar Shaikh are wanted.