What confuses you is this. Henry grew up in this house. He's known this staircase since he was a kid, like every corner of his house. He could have walked blindly through the whole house in the dark, no doubt about it. So something must have happened that day. Something unusual, out of the ordinary. Ask the people present a question about it. What was different about that day than it always was?
You were sure that everyone in the family would be ready to grieve in public and swear how much they loved Henry. However, now it seems to you that some don't even plan to do that. It seems as if everyone's lives have become easier with the old man gone. Try to understand who and how they really felt about him. Watch what they say and turn on all your professional skills. Someone is definitely lying here!
LIST OF PERSONS WHO WAS IN THE HOUSE AT THE TIME OF THE INCIDENT: