Keep the killer's secret between you and the killer

No. You bring the story, from a boxed kit or your own head, and type in each character. Joinue handles the casting: the private cards, who gets which, and sending them all out at once.

Choose Murder Mystery, write each guest's card on the cast board and tap Release. Everyone gets their own card at the same moment and can't see anyone else's. Only hosts see the whole cast.

No. Only the host needs a free account. Guests RSVP from the invite link and, once you send the cards, open theirs on that invite, on the phone they answered from. If they left an email, they're told it's ready.

Yes. Once the cards are out, the board marks every card Opened or Not opened, including guests who answered from the link.

Yes. Edit the card and only that guest is told; it shows as unopened until they read it again. To rework several, hide every card, fix them, and send them again.

Not as a suspect, really. The host can see every card, so most hosts play the narrator, the detective or the victim. A co-host can share the writing.