Horne was testifying during the third and final day of a hearing where he and current aide Kathleen Winn are trying to fend off civil allegations of illegal campaign coordination.
Under questioning by his attorney, Michael Kimerer, Horne repeatedly said he broke no campaign laws.
"We absolutely never coordinated or violated any of the laws," he said. "I absolutely never did coordinate with Kathleen Winn."
Horne said that while he did send an email to Winn urging her to raise another $100,000 from a national Republican group, he made a legal distinction between helping an independent committee raise funds and telling it how to spend the money or helping it design an ad, for instance.
"You're prohibited from communicating about the expenditures ... but there's no prohibition about talking about the money, the contributions," Horne said.
But that email, besides containing a request for Winn to raise more money, also contained polling and strategy information, and she passed that on to her campaign consultant.
Judge Tammy Eigenheer of the Arizona Office of Administrative Hearings is overseeing the case, but it will be nearly two months at best before she issues a ruling. First, lawyers for both sides will file written closing arguments.
Her ruling will likely not be the end of the case, however, because Yavapai County Attorney Sheila Polk can accept or reject her findings and impose sanctions herself. She determined in October that Horne violated the law and must repay $400,000 to donors and pay three times that amount in fines.
Horne and Winn could appeal any decision, dragging any final conclusion into the election season, where Horne faces a challenger in August's Republican primary as he seeks a second term. If he wins the primary, he'll likely face the same Democrat he narrowly defeated in 2010, Felecia Rotellini, a former prosecutor and bank regulator.
Horne and Winn are accused of working together on a campaign ad targeting Rotellini that was paid for by an independent group Winn was running, Business Leaders for Arizona. That "coordination" is illegal in Arizona.
Winn testified Wednesday that she had become friends with Horne during the primary campaign but told him she would stop work on his official campaign to instead help raise money and spend it independently in the general election.
Winn said when she told Horne about her plans in early October 2010, he advised her on campaign finance laws dealing with outside groups and referred her to a lawyer, who gave her advice on what she was allowed to do.
She acknowledged speaking with Horne regularly, but not about her campaign efforts. Prosecutors believe that there is evidence on specific days of illegal coordination, citing calls with Horne on a day when an ad was finalized with a political consultant. Winn says she and Horne only spoke about a real estate transaction that day, which is not illegal.
"I even asked my attorney if I could talk to Tom Horne, and I could talk to Tom Horne, just not about this campaign," Winn said under questioning from her lawyer, Timothy La Sota.
Yavapai County prosecutors are trying to show that Winn consulted with Horne before giving final approval for the ad targeting Rotellini. They point to a series of emails and phone records showing Horne communicated with Winn as she was giving final approval for an ad campaign overseen by consultant Brian Murray. They acknowledge the evidence against the pair is purely circumstantial.
An FBI agent this week testified that the emails and cellphone records show Horne talked to Winn while she worked with a campaign consultant about an ad.
Both denied they ever discussed campaign strategy or the content of the TV ad.
"Tom was not involved in the process of this ad," she told Deputy County Attorney Jack Fields. "I don't know how many different ways I can say this."
But lawyers for Horne and Winn scored major points Tuesday when a witness, Greg Tatham, disputed FBI agent Brian Grehoski's assertion that Tatham said Winn wasn't involved in the real estate deal with Horne.
Tatham, whose wife is a former Horne spokeswoman, had tape-recorded two calls with the agent and his partner, and Winn was mentioned in neither.
Grehoski returned to the stand Wednesday and said there was an additional phone call where Tatham was asked about Winn's involvement in the deal.
"In my opinion he is either lying to you or he doesn't recall it too well," Grehoski said.
He was met with skepticism from defense attorneys.
Defense attorneys say Winn, who used to work in real estate, and Horne did discuss a real estate deal during the period under investigation. But Grehoski said none of the emails he has reviewed show they were discussing real estate.
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