I'm inside, what can I do?

Hint 1 of 5:

Look very carefully at EVERYTHING.

Hint 2 of 5:

Move things around if you have to.

Hint 3 of 5:

Read the note on the coffin.

Hint 4 of 5:

Move the body in the foreground.

Hint 5 of 5:

There's a key under the dead body.