What three things act on decaying organisms to form fossil fuels

The fossil fuels form from the buried remains of ancient organisms, formed from the remains of dead plants and animals.
These plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the earth's crust over hundreds of millions of years. So, three things that act on decaying organisms to help form fossil fuels are:
-pressure
-heat
-physical and chemical changes
People  use fossil fuels products for transportation and heating, many power plants burn coal for heat to turn turbines that generate electrical energy. ...

They are like other investigations? say there was a murder u have to do blood test and finger prints which run through a lab.