Washington (CNN) President Donald Trump's associate Roger Stone repeatedly lied to Congress about contacts with WikiLeaks because the "truth looked bad" for Trump and his 2016 campaign, according to federal prosecutors.

Stone is on trial in Washington for charges that include lying to Congress, witness tampering and obstructing justice in a case that stems from former special counsel Robert Mueller's investigation into Russian interference in the 2016 election. He has denied all wrongdoing.

In his opening statement, prosecutor Aaron Zelinsky charged that Stone lied because the "truth looked bad for the Trump campaign and the truth looked bad for Donald Trump." Zelinsky said that Stone told five categories of lies to the House Intelligence Committee including about requests to get emails from WikiLeaks founder Julian Assange.

The case, Zelinsky said, is not about who hacked the Democratic National Committee server or whether Stone had contacts with Russia, but rather about his false testimony and efforts to obstruct the investigation.

The Justice Department alleged Wednesday -- the second day of Stone's trial -- that he "repeatedly lied under oath" and then sought to "cover up" his deception by tampering with a witness in a forceful opening statement.

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