When Maddy is about to yell at her Mother, she pulls out one of her ear buds. But when the camera shows Maddy again both of them are back in.
It takes temperatures of over 1100° C and several hours to burn bone. There is no possible way to burn a body to ash in a house fire.
Ethyl ether burns at 160° C (320° F) about half the temperature claimed by Rigsby and 2° C lower than the temperature at which skin burns.
Burn injuries are essentially caused by the boiling of the liquid in flesh, not by actually burning. For example, a soldering iron would cause a severe burn but there is no flame involved.
It is impossible to contaminate a crime scene that has been burnt, then extinguished by firefighters, over several hours. Especially not after it's been walked through to remove the body.
All trace evidence is destroyed by the fire and/or washed away.
Ethyl ether is not uncommon or difficult to work with. It's a widely available solvent and the only requirements for its safe use are don't ingest it and open a window.
Arsonists do not like to watch the fire "even more so when coupled with murder".
Arsonists don't kill on purpose, their sole interest is the beauty and power of fire for its own sake, not as a tool. People who use fire to kill or destroy evidence are not arsonists, they're just murderers.
Dave Martin was known to many people in the community. Mitchell Reese operated a business and would also have been known to many people in the community. It makes no sense for Reese to be suspected of being Martin. He would have been recognized.