"I think there's more and more evidence that implicates Russia," the Indiana governor said on NBC's "Meet the Press."
His comments are notable because Trump has insisted it's not clear whether Russia is playing a role.
In the second presidential debate, he said Clinton's campaign has pointed to Russia's role in the hacking as a political deflection.
"But I notice, anytime anything wrong happens, they like to say the Russians are -- she doesn't know if it's the Russians doing the hacking," Trump said. "Maybe there is no hacking. But they always blame Russia. And the reason they blame Russia because they think they're trying to tarnish me with Russia."
On Friday, US officials familiar with the investigation told CNN there is mounting evidence that the Russian government is supplying WikiLeaks with hacked emails pertaining to the US presidential election.
The methods of the disclosures "suggest Moscow is at least providing the information or is possibly directly responsible for the leaks," one US official said.
US intelligence officials are still investigating the degree of connection between Russia and WikiLeaks but they remain confident that Russia is behind the leaks themselves.
CNN attempted to reach WikiLeaks for comment but received no response. WikiLeaks's founder, Julian Assange, has previously denied any connection to or cooperation with Russia.
On Friday, former Acting CIA Director Mike Morrell said on a conference call organized by the Clinton campaign that it was "absolutely clear ... WikiLeaks and Guccifer 2 are working with the Russians on this."
Russia's highest officials are dismissing accusations that Moscow is trying to sway the US presidential election with cyber attacks, speaking out before the latest accusation concerning WikiLeaks was shared with CNN on Thursday.
President Vladimir Putin ridiculed such talk Wednesday as "hysteria."
"Let them prove it," Sergei Lavrov told CNN's Christiane Amanpour, waving off a US vow to retaliate with a "proportional response."