The 88-year-old business investor and Holocaust survivor has been a frequent target for his left-leaning political involvement.
"It's almost like an umbilical cord," one politician said.
The suspect, 37, had a prior relationship with the victim, authorities said.
The Oct. 3 shooting killed another officer and left five others wounded.
Selling escalated from Wall Street into a heavy selloff in Asia before hitting Europe, which was facing a fifth straight day of declines.