
Abhisit said reports over the case submitted separately by Deputy Prime Minister Suthep Thaugsuban and Deputy Police Chief Pol Gen Thani Somboonsap, head of the investigation team, contradicted each other on several points.
He said he will have evidence from all parties compiled and the case should be more transparent early this week.
What the government is doing is to move the investigation ahead and take legal action against the culprits.
Sondhi, a key leader of the People's Alliance for Democracy (PAD), was ambushed by gunmen in a pickup on his way to work on early morning of April 17. He was wounded by gunfires.
Meanwhile government-run Thai News Agency quoted Suthep as saying that the decision to sack National Police Chief Pol Gen Patcharawat Wongsuwan from his post rests solely with the prime minister.
Speaking while visiting his hometown province of Surat Thani, Suthep said his reports were based on "principle and law" and that he would not allow any group to pressure the government to dismiss the national police chief from his post.