The rejection of the National Anti-Corruption Commission's prosecution demand means further study by a joint panel of the NACC and the Office of the Attorney-General, which said there was not yet enough evidence to take the former prime minister to court.
The NACC submitted its investigation report to the OAG, recommending that it take legal action against Ms Yingluck for malfeasance on the grounds she had allowed corrupt practices in the rice-pledging programme to continue, despite having knowledge of it as ex-officio chair of the rice policy committee .
OAG spokesman Wanchai Rujanawong said that after receiving the case from the NACC the OAG set up a subcommittee chaired by deputy attorney general Wuthipong Wibulpong to study it.
The subcommittee found the investigation report to be incomplete on three points.
On the conclusion that Ms Yingluck did not stop the programme despite knowing of the corrupt practice, since the rice-pledging scheme was one of the Yingluck government's policies delivered to the House of Representatives as required by the 2007 constitution, he said the NACC should have supplied sufficient evidence to point out whether Ms Yingluck had the power to stop the policy scheme.
On the alleged neglect of duty on the part of Ms Yingluck, the NACC should have had evidence to show how Ms Yingluck had failed to take action after being notified by the graft agency and the Office of the Ombudsman of the corruption during the implementation of the scheme.
Concerning the alleged corruption, the NACC should look for more witnesses to establish where in the implementation process the corruption occurred.
Moreover, in referring to a report of the Thailand Research and Development Institute (TDRI) concerning the alleged corruption, the NACC did not attach details, but only the cover of the report.
Mr Wanchai said attorney general Trakul Winitnaiyapak has ordered the OAG and the NACC to appoint their representatives to form a joint working committee to gather stronger evidence and complete the investigation report.
The representatives of the two agencies must be named in 14 days.
There is no timeframe for the working committee to complete its work. How long the investigation will take is not immediately known, Mr Wanchai said.
Mr Wanchai said if the case is to be forwarded to the Supreme Court's Criminal Division Division for Holders of Political Positions, it must be clear beyond doubt where in the process the corruption took place and when, and who were involved. After that the court would decide the case.