Cassamá was President Nino Vieira's spokesman at the time of the 1998–1999 civil war. After Prime Minister Francisco Fadul compared Vieira to Antonio de Oliveira Salazar during a visit to Portugal on April 19, 1999, Cassamá criticized Fadul for the use of "purposely offensive, aggressive language". Following the civil war, in which Vieira was ousted, Cassamá was arrested along with Conduto de Pina in early February 2000 for allegedly inciting war and supporting foreign occupation. He was later charged with embezzlement along with a number of others who had served under Vieira, but was acquitted by the Regional Court in Bissau in early June 2003. He subsequently served as President of the PAIGC Parliamentary Group. Although PAIGC repudiated Vieira, Cassamá was among those who welcomed Vieira back to Bissau when he returned from exile on April 7, 2005.