The latest on Sri Lanka's bombing investigation

One of the Sri Lanka suicide bombers was previously arrested by police and then released, a senior Sri Lankan government spokesman told CNN Thursday.

Ilham Ahmed Ibrahim -- one of two sons of a spice tycoon who blew themselves 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 bomb attack who was released earlier," Gunawardana said.

Ilham Ahmed Ibrahim and his brother Imsath Ahmed Ibrahim were previously identified as two of the suicide bombers in Sunday's attacks, which left at least 359 people dead across the country.

Police have confirmed to CNN that they are holding the brothers' father, Mohamed Yusuf Ibrahim, a wealthy spice trader, on suspicion of aiding and abetting his sons.

Police spokesman Ruwan Gunasekera said the elder Ibrahim was is in custody, as are all other members of the Ibrahim family police are aware of in the country.

CNN has not been able to reach Mohamed Yusuf Ibrahim or other members of his family for comment.

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Israel's Counter-Terrorism Bureau issued a travel warning for Sri Lanka on Thursday, raising the threat level to indicate a "high concrete threat," advising travelers to leave the country and avoid visiting Sri Lanka in the near future. 

The elevated alert level comes after consultations with security and foreign ministry officials, according to a statement from the Counter-Terrorism Bureau.

Level 2 is the second-highest threat level. A threat level of 1 indicates a "very high concrete threat" in which travelers are urged to leave the country immediately.

Some of the suspected attackers responsible for the Easter Sunday bombings in Sri Lanka were being monitored by the country’s intelligence services, Sri Lanka’s Prime Minister Ranil Wickremesinghe told CNN's Ivan Watson in an interview Thursday.

There was not "sufficient" evidence to put the suspected attackers in custody prior to the attacks, Wickremesinghe said.

He reiterated that the attackers were middle- and upper-middle class and had been educated abroad. He added that the profile of the suspected bombers was "surprising."

A prominent spice trader and father of two suicide bombers, Mohamed Yusuf Ibrahim, is in custody on suspicion of aiding and abetting suspects, Sri Lankan police spokesman Ruwan Gunasekera tells CNN.

Ibrahim is the founder of Colombo-based Ishana Exports, which describes itself on its website as the "largest exporter of spices from Sri Lanka since 2006."

Ruwan Gunasekera added that all other members of the Ibrahim family are believed to be detained.

Ibrahim was among dozens of people arrested in the wake of the attacks.

Sri Lankan national police spokesman, Ruwan Gunasekera, tells CNN the country’s Criminal Investigation Department (CID) has raided 5 safe houses connected with terrorists in the following areas:

The safe houses have now been sealed for forensic investigation.

Meanwhile, police say search operations have increased today and searches are currently underway across Colombo, including the set-up of roadblocks.

Police have asked the public not to panic, a police spokesperson told CNN.

All Catholic services across capital city Colombo have been suspended until April 29 because of security concerns, according to Fr. Edmond Tillekeratne, media director of the Archdiocese.

The decision was made at the direction of Archbishop of Colombo, Cardinal Malcolm Ranjith. 

Sudesh Kolonne's is one of hundreds of families destroyed by acts of unspeakable violence wrought on worshipers and tourists on April 21, Easter Sunday.

On the morning of the attack, Kolonne's family was at St. Sebastian's Church in Negombo, north of the capital Colombo, when a suicide bomber detonated an explosive. The blast killed dozens of people, including Kolonne's wife and daughter.

"These two were so excited that Sunday we'd go to church for the ceremony," he told CNN's Ivan Watson, fighting back tears. "Both died in front of me."

He showed CNN the last video he ever made of his daughter, singing a song to her father as she played an oversized guitar.

"She loved to sing, she loved to dance. She loved to create songs, you know?" he says.

"We had a really good family, especially my daughter. Now they're gone. It's very hard."

See more of his story here.