"While dead men can tell no tales, so illiterate men can write no diaries. Many of the Asian romusha were illiterate; poor, helpless peasants mostly forcibly conscripted - or callously lured by false promises of riches - and unaware of their ultimate destinations. While it is a matter of dispute as to whether Japan ever made any efforts to observe the Geneva Conventions on POWs (certainly the experiences of the POWs led them to believe that the Conventions were being deliberately ignored), the records kept of POW movements - for example from Singapore's Changi prison to Thailand, or from Thailand to Japan proper - suggests that at some perhaps higher levels, the intention of Japanese bureaucrats (as opposed to military staff on the ground) was, indeed, to keep accurate records of the POWs' fate as obligated under the Conventions. However, no such Geneva Conventions existed to govern the impressing or treatment of civilian labour; few official attempts were made to record the fate of Asian romusha.'
So begins the fascinating study authored by David Boggett. Well worth reading, this in-depth discourse sheds light on the horrific slave labor conditions of the real River Kwai captors and camps.
http://www.aiipowmia.com/wwii/thaiburma.pdf