A potential candidate in Indonesia's presidential polls on Tusday visited a memorial at MacDonald House, the site of a 1965 bombing, placed flowers and prayed at the marker in Orchard Road.
A day before in Jakarta, Dr Dino Patti Djalal, 48, had laid flowers at the graves of the two marines who carried out the bombing.
He told The Straits Times his "double laying of wreaths is to highlight the fact that this issue is sensitive to both nations".
"It's a painful period for both of us. Given the fact that this issue has somewhat recaptured public imagination... I think it's important to do this act of laying the flowers at the graves of Usman (and) Harun (the two marines)."
Referring to then Prime Minister Lee Kuan Yew's conciliatory gesture in 1973, when the Singapore leader sprinkled flowers on the graves of the two marines in Jakarta, Dr Djalal said: "I realise as I look at the issue, one thing that remains to be done is for an Indonesian to pray at the site of the bombing because they are innocent victims. So this is the purpose of my visit."
His act comes a week after two Indonesian marines posed as Usman and Harun at an international defence event in Jakarta.
It prompted Singapore's Ministry of Foreign Affairs to express concern and disappointment, and Indonesian leaders to express regret over the act and clarify that there was no policy to carry it out.
The controversy, however, began last month following Indonesia's decision to name a new frigate KRI Usman Harun, after the two bombers. The move drew protests from Singapore and strained bilateral ties.
The two men were convicted and executed in Singapore for the bombing, which killed three civilians and injured 33 others. But they were made national heroes in Indonesia in 1968.
Dr Djalal stressed that his visit to Singapore was a personal one, and his laying of flowers was a "people-to-people gesture".
The former Indonesian ambassador to Washington is a participant in the ongoing presidential convention of Indonesia's Democratic Party. He is known to be a close ally of President Susilo Bambang Yudhoyono, having been a presidential spokesman for foreign affairs.
But on Tuesday, he rejected suggestions that his visit was linked to the April 9 legislative elections in Indonesia - an important precursor to the country's presidential polls in July.
He said: "If this were a political thing, I would just play it safe because this is something that is not going to please everybody.
"But I call this the politics of doing the right thing, and my thesis, as an Indonesian young leader, has always been that leaders must do not what is popular but must shed light on events, and must do the right thing."
He also said it was "totally inappropriate" for the two marines last week to pose as the bombers, especially as it was done at an international forum.
Adding in Bahasa Indonesia, Dr Djala said the bombers were heroes because as soldiers, they had carried out their task. But he also prayed for the three Singaporean civilians who perished as they "did no wrong".
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