"Best way" to contact vacant owner

[James Green]

I've found a "great" vacant house in a popular area of Washington DC. After doing a LOT of sleuthing, I'm "pretty sure, 90% positive" that I've found the daughter of the deceased owner. I actually have her phone number, address.

Here's my question, should I go ahead and call her?! Or send her a letter/postcard?

If I call her, what should I say, how should I start it off?

Anybody here with any experience doing this?