Investigators are still trying to find out who sent a series of suspicious letters to at least five hotels near the site of the Super Bowl.

NYPD Commissioner Bill Bratton told the Daily News of New York Saturday (http://nydn.us/1fyjUcN) that New York Mayor Bill de Blasio also received a letter, but a spokeswoman for the police department says that the letter did not contain powder.

It wasn't immediately clear where that letter was sent or who received it. The mayor's office didn't respond to a request for comment.

Bratton says the letter to de Blasio arrived the same day suspicious powder was mailed to at least five New Jersey hotels near the Super Bowl and to the office of former Mayor Rudolph Giuliani.

Authorities said the powder appeared to be harmless.