Northern Ireland police have written to a number of Sinn Fein representatives and members as part of an investigation into a protest that stopped an Orange Order (a Protestant fraternal group) parade from passing through the mainly Catholic Garvaghy Road area of Portadown, the party confirmed on Thursday. The march had been cleared by the High Court for the first time in 28 years, and Sinn Fein leaders, including First Minister Michelle O'Neill and party president Mary Lou McDonald, joined the demonstration; the Democratic Unionist Party, Sinn Fein's partner in the power-sharing government, has demanded prosecutions, saying no one is above the law. The dispute matters because parades on the route fuelled unrest before the 1998 Good Friday Agreement, and it has now become a political crisis straining Northern Ireland's devolved government.