GUATEMALA CITY (Reuters) - A fraud trial against the brother and son of Guatemalan president Jimmy Morales began on Wednesday amid a scandal touched off by the president’s attempt to expel the leader of a U.N.-backed anti-corruption unit investigating the case.

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Guatemala’s top tribunal, the Constitutional Court, ruled definitively on Tuesday against Morales’ internationally criticized push to expel from the country Ivan Velasquez, the Colombian who leads the International Commission Against Impunity in Guatemala (CICIG).[nL8N1LF4RY]

The CICIG and the prosecutor’s office accuse Samuel “Sammy” Morales, the president’s brother and one of his closest advisers, and Jose Manuel Morales, one of the leader’s four sons, of facilitating false receipts that defrauded the national property registry in 2013, two years before Morales was elected. They deny any wrongdoing.

Neither of the two gave a declaration before a judge on Wednesday, where they appeared together with another 20 other defendants.

The scandal has hurt the popularity of Jimmy Morales, a former comedian, who won election in late 2015 after riding a wave of public discontent over the corruption scandals that brought down his predecessor Otto Perez Molina.

The president has said the investigation into his family was not related to his controversial decision to declare Velasquez “persona non grata.” Last week, Velasquez and Guatemalan Attorney General Thelma Aldana asked to remove Morales’ immunity, in order to investigate him for accusations of illegal campaign financing.

The case involves payments linked to the mother of Jose Manuel Morales’ then-girlfriend in 2013.

She allegedly sent the national property registry a $12,000 bill made out in the name of a local restaurant for 564 breakfasts, according to the attorney general. The breakfasts were never delivered.

Samuel Morales recognized the acts as a “favor” to his nephew, but he denied that he had benefited or been implicated in the network of fraud that deprived the institution of thousands of dollars.

Both were detained in January, then put under house arrest and barred from leaving the country.