Answer:
The maid, since there's no mail on Sundays.
They knew he didn't kill himself because the tape was at the beginning, so the killer rewound it after he was dead.
Mr. Thomas, since he wouldn't have exams to grade on the first day of school.
None. They never said the plane was crashing.
Look at the dates. They died of old age.
The married people, since they're not single.
She hopes the man will attend her sister's funeral.
None, since the others would fly away at the sound of the shot.
The newspaper delivery man, since there's no Tuesday or Wednesday paper and they would know there's no one alive to deliver them to.
Stop imagining.
A skull.
She shot him with a camera and developed the photo.
A coffin.
The living room.
Nothing.