<P> President Barack Obama addressed the nation after the attack . He said that the perpetrators were still unknown, but that the government would "get to the bottom of this" and that those responsible "will feel the full weight of justice". He ordered flags to half - staff until April 20 on all federal buildings as "a mark of respect for the victims of the senseless acts of violence perpetrated on April 15, 2013 in Boston, Massachusetts ." </P> <P> Moments of silence were held at various events across the country, including at the openings of the New York Stock Exchange, NASDAQ, and NYMEX on the day after the bombing . Numerous special events were held, including marathons and other runs . </P> <P> The bombing was denounced and condolences were offered by many international leaders as well as leading figures from international sport . Security measures were increased worldwide in the wake of the attack . </P> <P> In China, users posted condolence messages on Weibo in response to the death of Lü Lingzi . Chris Buckley of The New York Times said "Ms. Lu's death gave a melancholy face to the attraction that America and its colleges exert over many young Chinese ." Laurie Burkitt of The Wall Street Journal said "Ms. Lu's death resonates with many in China" due to the one - child policy . </P>

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