"We have their confessions, both in writing and on video, which can be presented in court hearings," Sombat said.

Earlier this year, Prachuap Hinkaew and Saneh Lekluan succumbed to chronic diseases while awaiting trial in prison.

Jon Lerwitworapong, who heads the Corrections Department's hospital, said Prachuap, 41, died of a serious fungal infection in his lungs and fungal meningitis on March 21, while Saneh, 44, died of blood-circulation failure on July 28.

"Both of them had infections that were too serious to recover from," Jon said.

Bangkok Remand Prison chief warden Thanapat Jantarapannnik said the families of Prachuap and Saneh did not suspect any foul play in their deaths.

However, Charoen's wife Korn-uma Pongnoi had expressed concerns that the pair might have been silenced to cut any links to influential persons who masterminded her husband's murder.

Before their deaths, Prachuap and Saneh confessed before investigators, prosecutors and lawyers that they killed Charoen out of personal vengeance. However, police also arrested three other members of the Hinkaew family for allegedly ordering the murder of Charoen.

In response to Korn-uma's concerns, Sombat said he had already assigned Pol Colonel Songsak Raksaksakul - who heads a division for special criminal cases - to investigate the deaths of Prachaup and Saneh and check if they were connected with any effort to silence the suspects.