The Department of Special Investigation has decided not to pursue lese majeste charges against red shirt co-leader and Pheu Thai list MP Jatuporn Prompan and other core members of the red shirt movement.
Nineteen red shirt leaders had been accused of offending the monarchy in violation of Section 112 of the Criminal Code.
The allegations stemmed from a United Front for Democracy against Dictatorship rally on April 10 last year to mark the first anniversary of the deadly clashes between soldiers and red shirt protesters at Kok Wua intersection on Ratchadamnoen Klang Avenue.
Pheu Thai Party list MP Payap Panket was also among the accused.
DSI chief Tarit Pengdith said that a meeting of the agency's investigators and prosecutors had recommended that lese majeste charges against the 19 be dropped as their speeches at the rally were not in violation of Section 112 of the Criminal Code.
However, the DSI has forwarded the case and its recommendations to the prosecution for further consideration.
It is up to the prosecution to decide whether to dismiss the charges as recommended by the DSI or to proceed with the case and question additional witnesses, Mr Tarit said.
Speeches made by Mr Jatuporn and other suspects cannot be published as the prosecution had yet to decide on the DSI's recommendations, he added.
Democrat Party leader Abhisit Vejjajiva yesterday expressed his concern about the DSI's decision not to indict the 19 red shirt leaders.
He insisted that their comments during the rally last year were obviously inappropriate.
Mr Abhisit also noted the DSI's decision coincided with rumours that Mr Jatuporn was tipped to become deputy interior minister in the expected cabinet reshuffle.
Meanwhile, Mr Tarit yesterday said the DSI has recommended a number of prosecutions in an alleged plot to overthrow the monarchy. The prosecutions are the result of a so-called conspiracy chart compiled by various security agencies that listed 39 suspects involved in a network to topple the royal institution.
The chart was released to the public by the Centre for the Resolution of the Emergency Situation on April 26, 2010.
Twenty-three of the suspects were later investigated by the DSI.
The DSI has recommended to the prosecution that some of them be indicted while charges against others be dismissed, Mr Tarit said, without giving exact numbers.
The agency is now waiting on the prosecution to respond to its recommendations, he added.