Sheila shot her parents at about 3 am.Seems to me the 50% detection figure on "people known to have fired a gun" is not a useful statistic for a person proposed to have fired tens of rounds from a blowback operated rifle.
It is probably not known when she killed the twins.
She had time to consider a range of mortal questions until she was seen by the police moving in the windows some time later.
Maybe she washed her hands like Lady MacBeth.
