Apparently it was a 39 y/o man who started screaming, the police jumped on him and the public started moving. On that moment a man dropped his suitcase and people started screaming that there was a bomb in it, so even more panic. Some fences fell over, which sounded a bit like gun shots so the panic was complete.
Accordomg to the head of the police of Amsterdam, Mr. Bernhard Welten, it was the Queen herself who insisted that the ceremony should be resumed. So she returned, after a few minutes. She was walking arm in arm with her son, and was holding the hand of princess Maxima. During the national anthem, the Queen had to fight her tears, as many others had to.
Afterwards the royals visited the wounded who were nursed in the Groote Club. When the queen was on her way home she heard that some people were also nursed in the royal palace, so she decided to go back, to visit them too.
The man that caused the panic is known by the police and has been convicted for violance and drugs related issues. He was dressed like an orthodox jew, supposedly not because he is one. Apparently the police can only keep him for a few hours, as the offence is 'disturbing public order'. But before they release him he needs to have a psychological examination. The man with the suitcase had nothing to do with the whole thing.
Tonight the Queen attended the traditional liberation day concert, where she was cheered extra loud, it seemed.