A few weeks ago we reported that an Irish owner of a GSM Samsung Galaxy S III claimed that his phone caught fire while sitting in his car dock. At the time we reported the story we hinted that it might be a hoax, and it seems we called it right. Apparently, after investigating the device, it was determined that the device was heated externally, likely in a microwave to get it to catch fire the way it did. Here's a quote with some additional details,

An investigation into the matter, conducted by Fire Investigations UK (FIUK), has revealed that the heat that damaged the phone was generated by an external source and not the device itself, ZDNet‘s Karen Friar said. During their analysis, FIUK’s tests analyzed not only the damaged smartphone, but other Galaxy S III units as well.

“The device was not responsible for the cause of the fire,” the investigators ruled, according to Friar. “The only way it was possible to produce damage similar to the damage recorded within the owner’s damaged device was to place the devices or component parts within a domestic microwave."
After the investigation, the user retracted his story and said that he was "mistaken" and revealed what really happened. Here's another quote with a final summation,

Following the FIUK findings, the user retracted his original statement, posting that there was no fault with the phone and that the damage had been caused by “another person” who apparently had been attempting to dry out the device. The user said that it was “not a deliberate act but a stupid mistake,” and the original thread — which contained photos of the damaged Galaxy S III, is no longer available online, Friar said.
It's funny what people will try to get away with... perhaps he should have simply opted for the insurance/replacement plan with his carrier beforehand if there was the potential for someone in his home to microwave it.

Source: S3Forums via RedOrbit