Explosives the Islamic State-linked group stocked for use in more attacks have been seized, police added.
The bombings killed 257 people and wounded hundreds at three churches and three hotels.
Seven suicide bombers died at their targets while another exploded his device later at a guesthouse after it failed to detonate at a leading tourist hotel. A ninth killed herself to avoid capture by police at her home.
Police have detained 73 suspects for investigation since the bombings and have seized stocks of explosives, improvised explosive devices and hundreds of swords.
They also found more than one hundred thousand dollars in cash in bank accounts connected to the group and another 40 million dollars worth of assets in land, houses, vehicles and jewellery.
Authorities have repeatedly said another attack from the extremist group was possible.
Sri Lanka's Catholic hierarchy closed churches for a second weekend on Sunday as the faithful celebrated Mass from home watching live on television.
But on Tuesday, one of the churches targeted in the attacks, St Anthony's Shrine in Colombo, opened part of the building to the public for the first time since the bombing.
Catholic schools remain closed after reports said two of their locations were to be attacked last weekend.
Government-run schools reopened for some students on Monday but many did not attend out of fear.
An army commander urged the public to resume normal activities and trust in the security forces.
The air force has warned that it will shoot down drones in the country's airspace if necessary, saying they are a threat to national security. Authorities banned drones after last month's attacks, but some have been operated in some parts of the country.
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