POA validity in case of death and the use of it after death of giver

Hello, My uncle gave a POA to DEVELOPER to build and sell property on his land with the condition to pay him back. But my uncle died and we suspect that the POA was used even after the death of my uncle (principle). Now because of a new twist we are been contacted by the delelopers partners. The POA HOLDER which also had a POA to handle the Parnership developer firm business died. Now they can utilize the POA. I would like to know even if the POA is EXCLUSIVE or SPECIAL (not general) will it be valid after death ? Also in my scenario isn't it criminal to use the POA after uncle death ?