As tenants in common, Ciro and Lucy bought an investment property together. Ciro sold his interest in the property to Walter. Walter died in an accident. Who now owns Walter's share?

Walter's heir

Explanation:

In united states' common law, the wealth which belonged to a deceased citizens will be automatically transferred to the closest family members (the heir), unless that person has made a legal document that specifically mentioned otherwise.

In this specific case, it does not mentioned that Walter has made a will or any prenup agreement before he died. So, Walter's share will be automatically transferred to his spouse. (in united states, spouse is considered the main heir after deceased)