The announcement of the arrest of Zarrar Shah — following Sunday’s detention of another alleged Mumbai plotter, Zaki-ur-Rehman Lakhvi and other alleged militants — could deflect intense U.S. and Indian pressure on Pakistan following the attack.

But much will now depend on whether Pakistan’s young civilian government keeps up the pressure on the militant groups that are believed to have been fostered by the country’s powerful security agencies.

Pakistan has targeted militants in the past, detaining some leaders only to quietly release them later, bolstering critics who claim Islamabad is not serious about fighting extremists.

Pakistani officials insist Islamabad’s old foe, New Delhi, has not shared any evidence with them that links the suspects to the attacks, raising questions as to how the country can bring them to trial. Islamabad has already said it will not hand them over to India.

Pakistani Prime Minister Yousuf Raza Gilani gave no details on Shah’s arrest except that he and Lakhvi “were in (Pakistani) custody and were being investigated.”

Both men are alleged to be members of Lashkar-e-Taiba, a banned Pakistani militant group blamed for other attacks on Indian soil and with historical ties to the country’s shadowy intelligence agencies.

On Wednesday, Indian police said they would question an Indian militant with known Lashkar links about the Mumbai siege. They said Nepal-based Sabauddin Ahmed was arrested in February with another militant who had scouted Mumbai targets a year before last month’s attacks.

Amitabh Yash, director of the police Special Task Force in India’s Uttar Pradesh state, said Ahmed managed safe houses in Nepal, using that country to smuggle Pakistani Lashkar members into India. Yash said he was able to take advantage of the fact that Indians don’t need passports to enter or leave Nepal. “He was their main point man in Katmandu, a very trusted man by Lashkar,” Yash said.