Sri Lanka's new government announced a probe Tuesday into 2019 Easter bombings that killed 279 people, saying that previous investigations had failed to identify other culprits responsible for the country's worst-ever attack against civilians.
In the aftermath, officials blamed a local jihadist group for the suicide bombings on three churches and three hotels, but a top Sri Lankan intelligence official was also accused of orchestrating the attack.
Other investigations faulted the authorities for failing to act on warnings from an Indian intelligence agency that an attack was imminent.
"There have been several commissions of inquiry, but some evidence was suppressed," foreign minister Vijitha Herath told reporters.
"We want to find out why there were irregularities in the previous investigations, take a fresh look at the incident, expose the culprits, and bring them to justice."
Herath's announcement came days after President Anura Kumara Dissanayake dismissed Sri Lanka's intelligence chief, Suresh Sallay.
British broadcaster Channel 4 reported last year that Sallay was linked with the bombers and had met with them prior to the attack.
A whistleblower told the network that he had permitted the attack to proceed with the intention of influencing that year's presidential election in favour of Gotabaya Rajapaksa.
Two days after the bombings, Rajapaksa declared his candidacy and won the November vote in a landslide after promising to stamp out Islamist extremists.
Sallay, who has denied any involvement in the bombings, was promoted to head Sri Lanka's main spy agency following Rajapaksa's win.
Sri Lanka's Catholic minority has maintained a campaign for justice since the bombings, saying that prior investigations failed to answer outstanding questions.
President Dissanayake on Sunday visited one of the churches targeted in the Easter Sunday attacks, where 116 people perished, and vowed justice for the victims.
"There is a widespread belief in society that the Easter Sunday attacks may have been carried out to gain political mileage," Dissanayake told the congregation.
More than 500 people were wounded in the bombings, which also killed 45 foreigners and crashed the island nation's lucrative tourism industry.
Last year, the Supreme Court fined then-President Maithripala Sirisena and four senior officials more than $1.03 million in a civil case for their failure to prevent the attacks.
The UN asked Sri Lanka in April to publish parts of previous inquiries into the bombings that had been withheld from the public.