Dutch police on Thursday arrested seven people on suspicion of preparing a terrorist attack in Amsterdam including a relative of one of the attackers who died in the 2004 bombings in Madrid. Earlier Thursday authorities sealed off a major Amsterdam shopping street as a result of the threat, while police conducted house searches. District Attorney Herman Bolhaar said those arrested include six men and one woman, aged 19-64. All are Dutch nationals of Moroccan ancestry. Police said the arrests followed a tip from Belgium about a possible attack with explosives. Bolhaar said none of the suspects were believed to have a history of terrorist involvement.