First, I would make sure it is not a scam. Second, I would get more information about the person who died, date of death, county where the property may be located etc. Then I would have an attorney do a preliminary check and if that leads nowhere, hire a private investigator.
Ms. James advises you correctly. Beyond that, one of the nice things about real property and about bank accounts (in addition to their monetary value) is that they leave somewhat of a paper trail -- for real property, there will be checks written toward the purchase, perhaps mortgage payments, property tax bills, maybe water bills, and the like. For bank accounts, there will probably be monthly or quarterly statements, interest statements, and similar types of documents.
If you know the general geographical area in which the decedent may have purchased real property, you can check with the county land recorder in those areas.
An attorney will, of course, have certain tools (and data bases) available that may not be available to you. So you may want to engage an attorney.
Good luck to you.
Michael S. Haber is a New York attorney. As such, his responses to posted inquiries, such as the one above, are limited to his understanding of law in the jurisdiction in which he practices and not to any other jurisdiction. In addition, no response to any posted inquiry should be deemed to constitute legal advice, nor to constitute the existence of an attorney/client or other contractual or fiduciary relationship, inasmuch as rendering legal advice involves the ability of the attorney to ask appropriate questions of the person seeking such advice and to thus gather appropriate information. In addition, an attorney/client relationship is formed only by specific agreement. The purpose of this answer is to provide the questioner with general information, not to outline specific legal rights and remedies.