1) To have a fall guy for the faked death of Steadman. 2) To draw out Michael and Linc's father. 3) To have the public see a nicely wrapped up execution. 4) To give a network television program a premise.
Sirens were fast approaching. It was Paul's only chance to get as far away as possible. Taking the extra time to execute Kim might have meant being captured...
The plan was that by the time they got results back on tests to the bones and blood...Michael and Linc would be in Mexico. This is merely a diversion, not a solution.