Ms Yingluck failed to appear before the commissioners yesterday (June 9) as scheduled and she asked to postpone the meeting without providing a suitable future date, said NACC member Vicha Mahakun.
The former premier and 33 other members of her government are accused of abusing their authority and acting dishonestly in paying costly compensation to the families of red-shirt protesters who were wounded or killed during political demonstrations from 2005 to 2010.
The B2 billion scheme had no legal basis to support it, commissioners ruled last month.
Mr Vicha added the person who hand-delivered the ex-premier's letter telling the commission she would not be attending was not properly authorised to do so.
According to the graft-buster, the letter carrier did not have an official document to prove he was authorised to represent her.
The man, Chaliew Dusadi, a lawyer from the Pheu Thai Party legal team, went to the NACC to deliver the letter for Ms Yingluck and declined to comment. "I am simply the messenger," he said.
In light of Ms Yingluck's failure to provide proper representation to hear accusations against her yesterday, or offer a new date, the NACC has set the new appointment for June 30.
Ms Yingluck will be notified by mail, Mr Vicha said.
Commissioners won't allow the former PM to seek another delay, he said.
"The NACC will follow its usual procedure and demand Ms Yingluck produce a defence statement in the next 15 days," Mr Vicha declared.
In another development, former senator Somchai Sawaengkarn, who chaired a Senate panel investigating the April 10, 2010, violence, testified before the NACC that victims of the crackdown during the 2010 red-shirt protests died at the hands of the so-called "men in black" group.
Mr Somchai is the last witness in the case against former prime minister Abhisit Vejjajiva and his then-deputy Suthep Thaugsuban over charges their orders to disperse red-shirt protesters led to more than 90 deaths.
Mr Somchai said he provided photographic and film evidence of the violent acts carried out by the men in black group, which his panel had collected in 2010.
He affirmed there were two to three groups carrying out violent acts on April 10, 2010, and the panel found evidence that they prepared C4 explosivses, which were then used on protesters on May 19, 2010.
According to him, eyewitnesses said the men in black used M-79, M-16 and AK-47 guns, as well as M67 and C4 explosives, which corresponds to wounds found on the victims.
In the case of Reuters journalist Hiroyuki Muramoto, who died covering the April 10 clashes, the bullet which hit him did not correspond to guns used by the military, Mr Somchai said.
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