Most supporters, experts & guilters agree that the burn marks were caused by Nevill's killer.
Bamber even used the burn marks in his 2012 appeal to claim the they were caused without the silencer attached.
Supporters claim Sheila suddenly stopped her uncontrollable rage, to be totally composed & calculated & stand by the aga. Although have not said who helped her lift Nevill onto the coal scuttle.
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It would have taken Sheila well over 5 minutes to heat the rifle using the aga. A big chunk of her 22 or 38 minute time window before the police arrived, considering the mountain of other things she was supposed to have done -
'How long does it take to heat metal?
With a high BTU plumbers torch and starting with a totally cold forge it may take 4 to 5 minutes. You'll know it is ready when the brick starts to glow bright orange inside. Play with it a bit and you'll learn when it's hot and when it's not'.
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Metal also does not melt so any rifle used would not look any different -
'No kerosene fire can burn hot enough to melt steel." The posting is entitled "Proof Of Controlled Demolition At The WTC." FACT: Jet fuel burns at 800° to 1500°F, not hot enough to melt steel (2750°F)'.