Ilham Ahmed Ibrahim – one of two sons of a spice magnate who blew himself up in Sunday's attacks – detonated a device at the Cinnamon Grand Hotel in Colombo, Sudarshana Gunawardana said.
"It was the suicide bomber of the Cinnamon Grand bombing that was released earlier," Gunawardana said.
Ilham Ahmed Ibrahim and his brother Imsath Ahmed Ibrahim were previously killed in at least 359 people during the Sunday attacks as two of the suicide bombers identified across the country.
The police have confirmed to CNN that they suspect the brothers' father, Mohamed Yusuf Ibrahim, a wealthy spice merchant, of supporting his sons.
Police spokesman Ruwan Gunasekera said the elder Ibrahim was in custody, as all other members of the Ibrahim family police know in the country.
CNN was unable to contact Mohamed Yusuf Ibrahim or other members of his family for comment.
In an interview with CNN, Sri Lankan Prime Minister Ranil Wickremesinghe said the alleged bombers were upper and middle class, well educated and educated abroad, a profile he described as "surprising". He added that some of them were being monitored prior to the attacks, but that there was not "sufficient" evidence of their detention.
Sri Lanka is facing a huge international criminal investigation. Six foreign police departments and Interpol support local police, including Scotland Yard from the United Kingdom and USA FBI from the United States.
Gunasekera told CNN that in Sri Lanka, Criminal Police (CID) and Terrorist Investigation Division (TID) officials have searched five safe houses across the country in connection with Sunday's attacks. These sites have since been sealed for forensic investigations.
More than 70 suspects were arrested on various charges, including terrorism suspicion, support and support for terrorism, and conspiracy to commit terrorism, Gunasekera said. He added that four senior suspects are being held by TID and 33 by CID.
Of those arrested, four suspects are female and all are Muslim. Gunasekera said most of them are family members and friends of suspected suicide bombers. None of the arrested is foreigners.
On Wednesday evening, major raids were carried out, in which 16 people were arrested at various locations near the capital, Colombo. Three shotguns and two walkie talkies were also confiscated.
As the police continued to investigate how a previously unknown terrorist group managed to conduct a large and coordinated series of attacks, Gunasekera also stated that the police had confirmed an explosion in predominantly Muslim territory in early Sri Kathankudi in Sri Lankas conducted a test run of the terrorists. In this explosion they blew up a motorcycle.
On Thursday, police announced that searches are being conducted throughout Colombo, including the construction of roadblocks. The police called on the public not to panic, a police spokesman told CNN.
Sri Lanka remains on alert, and in recent days numerous controlled demolitions of suspicious packages and vehicles have been carried out. Gunasekera, however, said he did not believe the controlled explosions on Thursday were explosives.