Accompanied by three other caretaker senators, Napinthorn arrived at the Crime Suppression Division in response to a summons.

Napinthorn denied any wrongdoing. He said he had no business or political conflict with Kobkul.

The senator was implicated because a  gunman admitted shooting Kobkul to repay Anantasak Srisawas - a member of Muang Ratchaburi municipality and the manager of Sri Muang Market, owned by Napinthorn.

"I don't know if Anantasak had any conflict with Kobkul," Napinthorn told police.

At the time of her death, Kobkul was about to open a new fresh-market.

Napinthorn yesterday insisted that his market had a solid base of customers throughout more than two decades and would hardly have felt any impact if Kobkul's market had opened.

"I am expanding my fresh-market business to Nakhon Sawan and Khon Kaen. Also, I have been discussing deals with companies like The Mall Group and Big C Supercentre. This year, I have already signed a Bt200-million deal with Tesco-Lotus," he said.

Pol Lt-General Montree Jamroon, the chief investigator in the case, said his team would take about two more weeks to conclude the probe.

"So far, we have both witnesses and circumstantial evidence," he said without elaborating.