Story highlights The September 4 email was sent during the final stretch of the 2016 race

Congressional investigators are uncertain who the sender is

Washington (CNN) Candidate Donald Trump, his son Donald Trump Jr. and others in the Trump Organization received an email in September 2016 offering a decryption key and website address for hacked WikiLeaks documents, according to an email provided to congressional investigators.

The September 4 email was sent during the final stretch of the 2016 presidential race -- two months after the hacked emails of the Democratic National Committee were made public and one month before WikiLeaks began leaking the contents of Clinton campaign chairman John Podesta's hacked emails.

The email came less than three weeks before WikiLeaks itself messaged Trump Jr. and began an exchange of direct messages on Twitter. Trump Jr. told investigators he had no recollection of the September email.

Congressional investigators are trying to ascertain whether the individual who sent the September email is legitimate and whether it shows additional efforts by WikiLeaks to connect with Trump's son and others on the Trump campaign. The email also indicated that the Trump campaign could access records from former Secretary of State Colin Powell, whose hacked emails were made public by a Russian front group 10 days later.

The email, which was described to CNN by multiple sources and verified by Trump Jr.'s attorney, came from someone who listed his name as "Mike Erickson." It was addressed to Trump, Trump Jr., Trump Jr.'s personal assistant and others, and turned over to Congress as part of the documents provided by the Trump Organization.