The U.S. Securities and Exchange Commission is investigating companies associated with Bay Area real estate investor Kenneth J. Casey, who died last month.

Lawyers at Ragghianti Freitas last week sent letters to investors in Casey’s Professional Financial Investors Inc., a Novato, California-based real estate firm that touts more than 900 apartment units under management and over 600,000 square feet of commercial warehouse space in Marin and Southern Sonoma counties, and an associated fund, Professional Investors Security Fund Inc.