Pol Pot then fled his northern stronghold, but was later arrested by Khmer Rouge military chief Ta Mok, who subjected him to a show trial for the death of Son Sen.
Pol Pot fled to Thailand where he lived for six years under Thai protection.
The death toll from Pol Pot's policies is a matter of much debate.
The Cambodian army was defeated, and Pol Pot fled to the Thai border area.
On the night of April 15, 1998, the Voice of America, of which Pol Pot was a devoted listener, announced that the Khmer Rouge had agreed to turn him over to an international tribunal.
Immediately after the fall of Phnom Penh, Pol Pot began to implement reforms following the concept of "Year Zero" ideology.
In 1979, Pol Pot fled into the jungles of southwest Cambodia after an invasion by neighboring Vietnam, which led to the collapse of the Khmer Rouge government.
The Khmer Rouge then established a new stronghold area in the west near the Thai border, and Pol Pot relocated back into Cambodia from Thailand.
Internationally, Pol Pot aligned the country with the People's Republic of China and adopted an anti-Soviet line.
Saloth Sar called himself the "brother number one" and declared his nom de guerre Pol Pot, from the French Politique potentielle, as his official name.
In 1995, meanwhile, Pol Pot experienced a stroke that paralyzed the left side of his body.
After Son Sen attempted to make a settlement with the government, Pol Pot had him executed on June 10, 1997.
Pol Pot's legacy in Cambodia is one of mass murder and genocide on a scale unprecedented in relation to the size of his country.
Shortly after this, Pol Pot moved to China for medical treatment for cancer of the face.
Vietnam did not move decisively to root out the Khmer Rouge and used the continued existence of Pol Pot's forces to justify continued military occupation of Cambodia.