Thanks everyone, I like this film too, but the plot is weak in a few places. The fact that there are,conveniently, two suspects under investigation, and just because the other one ran and gets killed, Uncle Charlie is off the hook ? The other one is: how in the world would the niece explain her uncle's death on the train in a satisfactory and realistic manner without admitting the truth ? He just
"accidentally fell off the train??". Good movie though
RSGRE

What makes even less sense is that Uncle Charlie would freak out about that article in the newspaper. Why would he think anyone in the family would think the story was about him? If there was a photo of him, yeah, but otherwise it just made no sense.

I had to agree that this film was a bit lax about the plot and its development.
Still, great work by the director and cast. I especially thought Teresa Wright was great in this.

IMHO, the flaw was Uncle Charlie anticipating that Charlie would go out to the garage, alone no less, so he could asphyxiate her lame, lame, lame. And I love this film !!
I just try to not think about it

Devils Advocate: Maybe they didn't wanna spook him until they had a solid case. Bringing him in for questioning/printing/photographing and then some high $ lawyer getting him out from a temp holding cell might have been something they wanted to avoid. If they got his photo surreptitiously and a grand jury ran with it, it would have given a Judge enough to withhold bail.

Plots never really interested Hitchcock, and were more a means to the end(s), more than anything else.
Don't lend your hand to raise no flag atop no ship of fools.

I can't see two detectives deferring the arrest of a homicidal maniac for any reason.

Well, we know that that one detective had a thing for young Charlie. Maybe his wanting to get into the house to interview the family had more to do with meeting young Charlie than apprehending old Charlie. You think?

They explained it as having to do it carefully so that the mother wouldn't die of shock or something. Pretty weak, I agree.

His screenwriter was Thornton Wilder, not James Thurber.