The brothers of a Spanish journalist killed by US troops in Baghdad are backing a lawsuit against Prime Minister Jose Maria Aznar.
The Cousos want to haul the prime minister before the Supreme Court
The action is being brought by a coalition of anti-war groups, which accuse Mr Aznar of supporting the US-led invasion without the authority of the Spanish parliament or the head of state, King Juan Carlos.
Television cameraman Jose Couso, 37, died on Tuesday after a US tank fired on a hotel used by foreign journalists in Baghdad.
We want to know if we live under the empire of law or under the law of empire
Despite fierce popular opposition, Mr Aznar's conservative government has been one of the most vocal supporters of war.
Law of empire
Mr Couso's brothers also asked the Spanish Foreign Ministry to provide information about his killing and the diplomatic efforts to explain the incident.
"We want to know if we live under the empire of law or under the law of empire," they said at a press conference on Friday.
The lawsuit against Mr Aznar was filed last week by a number of groups - including Culture Against the War and the Free Association of Lawyers.
Justice Minister Jose Maria Michavila has dismissed the suit as "unfounded", saying the government acted in keeping with international law.
The Spanish Government has asked Washington to look into Mr Couso's deaths, as well as that of another Spanish journalist, Julio Anguita Parrado - who was killed on Monday by Iraqi rocket fire.