The investigation into the sudden appearance of a pornographic image on one of the monitor screens in the parliament chamber on April 18 has been completed, but the result is inconclusive, House deputy secretary-general Khamphi Ditthakorn said on Wednesday.

Mr Khamphi, who led the investigation, said he had received a letter from the manufacturer of the wi-fi enabled screen, LG Co of Korea, that there is no device to record connections between a wi-fi dongle attached to the LG monitor screen and a smart phone.  Once the phone is shut off, the data signal transmission was automatically erased.

Therefore, it was not possible to determine the number of the telephone used to upload the lewd  image to the plasma monitor screen in the parliament chamber.

Parliamentary staff in the audio-visual department were earlier exonerated of blame.

Mr Khamphi said the investigation was now regarded as completed,  because it was not possible to locate the transmission source of the photograph.

This would be formally reported to House Speaker Somsak Kiatsuranont, he said.

Mr Khamphi on Monday invited experts from CAT Telecom and parliament IT officials to investigate the April 18 incident.

It was found that Samsung Galaxy Notes and Samsung Galaxy Tabs were capable of sending signals to the plasma screen by using an "all share" application installed on the devices, without the need for a password.

However, the phone numbers of the senders could not be traced as the files were sent via wi-fi, the experts concluded.

LG was asked about this matter and its reply confirmed this, Mr Khamphi said.