Deputies say they received a 911 call at the Valencia Lakes community near Boynton Beach, Florida, just before 1 p.m. Thursday. There, deputies said they found Sondra Wiener, 87, and her 90-year-old husband dead from gunshot wounds.
Detectives said they believe deaths appear to be a murder-suicide.
Wiener was Madoff's sister.
Madoff pleaded guilty in 2009 to running a $65 billion Ponzi scheme. He died in a federal prison in North Carolina in April at 82 while serving a 150-year sentence.
Wiener's death is just the latest tragedy to beset members of Madoff's family.
Madoff's oldest son, Mark, hanged himself on the second anniversary of Madoff's 2008 arrest, leaving behind a bitter note.
His younger son, Andrew, blamed Madoff for the return of a rare cancer that killed him in 2014, citing the stress and shame he experienced from his father's fraud.
Madoff's Ponzi scheme was also linked to the suicides of three investors.
This story was originally published by Jason Davis on Scripps station WPTV in West Palm Beach, Florida.