The Democrat spoke with WPRO Tuesday - his first interview since Jeff Britt was charged Friday with money laundering and making a prohibited campaign contribution.
Britt's attorney says his client was used by the campaign as a "fall guy."
Authorities allege Britt funded a $1,000 contribution made through a third party to defeated Republican primary candidate Shawna Lawton, for a mailer endorsing Mattiello instead of her party's nominee.
Mattiello says he wasn't told about the mailer and wouldn't have allowed it to be sent. He says it cost him votes.
Mattiello says Britt did some things well, while other things "obviously we're not going to condone."
Information from: WPRO-AM, http://www.630wpro.com/
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