4月15日，在美国首都华盛顿白宫，美国总统奥巴马就波士顿爆炸事件举行记者会。

　　继16日截获一封寄给美国密西西比州共和党参议员罗杰·威克的带有致命蓖麻毒素的信之后，美国官方又截获一封带有同种毒素的信，而收信人正是当今美国总统奥巴马。

　　负责保卫总统安全的美国特工处发言人埃德·多诺万17日早些时候透露，该处截获的一封寄给总统奥巴马的信件含有“可疑物质”。这封16日收到的信是在远离白宫的一个邮件设施内被截获的。

　　稍后，美国联邦调查局进一步证实，初步测试表明寄给奥巴马总统的信中含有致命蓖麻毒素。

　　联邦执法官员向美国媒体透露，这封信与16日寄给参议员罗杰·威克的信“非常相似”，两封信来自同一个寄信人。美国全国广播公司报道称，联邦官员们表示，他们已知道寄信人是谁，但是还没有逮捕任何人，因为当局正在等待进一步的测试结果。

　　此前一天，美国国会领导人证实，一封寄给美国密西西比州共和党参议员罗杰·威克的信被截获，这封信被检测出带有被称为“最可怕的生物武器”的致命蓖麻毒素。

　　蓖麻毒素是一种只要极小的剂量就能致人于死地的毒素。如果吸入或吞服，致死剂量仅为1毫克，而如果进行注射的话，仅仅500微克此物质就能杀死一位成年人。

　　据美国福克斯电视台引述联邦调查局的一份通告称，两封信件上面都写着相同的一段文字。而且两封信的落款都是：“我是KC，我批准这一信息。”这一落款与奥巴马去年在竞选广告中的落款只有名字之别。

　　这两封可疑信件加剧了华盛顿以及全美各地的紧张局势。此前，15日发生的波士顿马拉松赛连环爆炸案尚未破案，该爆炸事件导致3人死亡，170多人受伤。

　　在波士顿刚刚发生恐怖袭击之际，有毒信件的出现，不禁让人想起“9·11”事件后的炭疽热威胁。但目前尚不清楚这两封信与波士顿马拉松赛爆炸案是否有任何联系。

　　Letter to Obama contains deadly ricin

　　The FBI confirmed on Wednesday a letter addressed to President Barack Obama has been preliminarily tested positive for ricin but the authorities have not found a link to Monday's Boston bombings。

　　"The envelope, addressed to the President, was immediately quarantined by US Secret Service personnel, and a coordinated investigation with the FBI was initiated," said the FBI in a statement。

　　The FBI said the suspicious letter addressed to Obama and filters at a government mail screening facility were both preliminarily tested positive for ricin on Wednesday. Mail from that facility is also being tested。

　　"Only a full analysis performed at an accredited laboratory can determine the presence of a biological agent such as ricin. Those tests are currently being conducted and generally take 24 to 48 hours," the FBI said。

　　A US Secret Service spokesman said on Wednesday that a letter addressed to Obama contained "suspicious substance."

　　The spokesman said that the authorities intercepted the suspicious letter at the White House off-site mail facility. The letter arrived on Tuesday, the same day that another letter addressed to a US senator was intercepted and initially tested positive for ricin, a highly toxic substance。

　　Two Senate buildings were evacuated on Wednesday morning due to reports of suspicious mails。

　　While the investigation into the letters remains ongoing, the FBI also said in the statement that there was no indication of a connection to the attack in Boston。

　　Lawmakers on the Capitol Hill confirmed Tuesday that the Capitol Police intercepted a suspicious letter, which was addressed to Senator Roger Wicker, at an off-site postal screening center on Tuesday morning。

　　The incidents came one day after two explosions occurred near the finish line of the Boston Marathon, killing three people and wounding over 170 others. The authorities have called the Boston bombings an "act of terror," but the motives and perpetrators remain unknown。

　　(英文部分来源：Xinhua)

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