On Wednesday, public prosecutors decided not to indict former Ratchaburi senator Napinthorn Srisanpang on charges he was behind the murder of Kobkul Nopamorn-bordee last May because of insufficient evidence.

Kobkul's husband Manit, along with their children and 80 Ratchaburi residents, submitted a letter via a Government House official asking premier Chulanont Surayud to order all agencies involved in the investigation to gather more evidence and bring the true culprits to justice.

The group later presented their request to national police chief Kowit Wattana via a secretary, asking for police to collect more evidence, check the current stock of evidence for holes and look into many suspicious circumstances. For example, the suspected gunman, Sangad Umake, died from poisoning right after his arrest warrant was issued.

Attorney-General Pachara Yuttithamdamrong said he would ask Sermkiat Woradit, director-general of the Criminal Litigation Department, why his prosecutors dropped the case.

If the police investigators on the case want to know the reasons for not pressing charges, they must submit a letter of objection signed by the national police chief. So far no such form has been received by the Attorney-General's Office, Pachara added.