German police detonated a suspicious-looking package sent to President Joachim Gauck\'s office.\"A controlled explosion was carried out in the park next to the presidential palace Bellevue,\" Reuters quoted a presidential spokesman as saying.\"An initial assessment showed it posed a concrete danger,\" he said.The incident came a day after US authorities charged a man with mailing letters to President Barack Obama and a US senator containing a substance that preliminarily tested positive for Ricin.