Speaking on a provincewide radio show, Prentice said backbencher Mike Allen took responsibility and pleaded guilty after he was caught in an undercover sting operation while on government business in Minnesota in 2013.
"He didn't lie about that. He accepted responsibility. He pled guilty," Prentice said Wednesday. "He received his punishment, served his punishment and, at the end of the day, basically fulfilled his responsibilities to society."
Allen is the Tory incumbent in Fort McMurray-Wood Buffalo in next Tuesday's election.
Prentice was challenged on why the PCs are allowing Allen to run, while they disqualified candidate Jamie Lall from running in Chestermere-Rocky View. Court documents show Lall had a restraining order against him in 2007 in relation to an ex-girlfriend. The order alleged Lall was abusive and threatening.
"(The restraining order) alone, from my perspective, means that he's not acceptable as a candidate for my political party, clearly," replied Prentice. "The second reason is that he was not forthright with the nomination committee who interviewed him about that. Two strikes."
Lall, who is running as an Independent and said he was frustrated by having his character besmirched, released texts from PC party executive director Kelley Charlebois and former justice minister Jonathan Denis this week.
Denis warned Lall in March not to talk to an individual hired by the PCs to vet potential candidates, because the party was trying to find a way to disqualify him.
"Buddy, you are being set up," Denis warned in another text. "Any further communication is with a lawyer.''
Lall wanted to challenge the current PC candidate in the riding, Bruce McAllister. McAllister and eight of his Wildrose party colleagues including then-leader Danielle Smith, crossed the floor to the Progressive Conservative government in December.
Lall has said he told the party about the restraining order as far back as 2012 and that it wasn't an issue for the party then. He has also said he and his former girlfriend are now on civil terms.
Denis himself resigned as justice minister at Prentice's behest over the weekend after he became embroiled in an unspecified legal dispute involving marital difficulties with his wife.
Asked to comment on Denis's role counselling Lall to get a lawyer and not co-operate with the PC party, Prentice said: "He's going to have to explain his emails."
Prentice was also asked if Denis is fit to run for the party based on his involvement in the Lall affair.
"He will have to explain his emails," Prentice replied. "People send all kinds of emails and I imagine that he will regret some of those in retrospect."
At a campaign event in Calgary on Wednesday, Prentice urged reporters to focus on the core issue of the election, rather than the Lall story.
"I encourage everybody who follows these matters, who writes about these matters, to get back to what's important to the province."
— By Dean Bennett in Edmonton