Special Counsel Robert Mueller's Russia report is set to be publicly released, with some redactions, on Thursday but Wall Street Journal Editorial Board member William McGurn says the American people still don’t know when the FBI investigation into the Trump campaign really began and called on Attorney General William Barr to appoint a grand jury to find out.

“This is still the open question. We don't really know when the FBI investigation began and what they were doing in the investigation,” McGurn, a Fox News contributor, said on "Fox & Friends" Wednesday.

“They're sticking to this idea that it was a conversation with (former Trump campaign foreign policy adviser) George Papadopoulos, but that increasingly looks suspicious and so forth. And I think the reason is, to cut through all this, it’s looking increasingly as though the FBI launched an investigation into a presidential campaign based on opposition research commissioned by Hillary Clinton, her team, and performed by a known Trump hater, Christopher Steele to spy on Trump people.”

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The Mueller report's Thursday release is expected to shed more light on the Russia investigation's conclusions, as reported by Barr, that the Trump campaign did not improperly collude with Russia, despite multiple attempts by Russian-affiliated individuals to involve the Trump team in computer hacking.

“It is a big deal when the FBI spies on any citizen, right? They're given these powers for a reason and it's a big deal. It's a bigger deal when you launch one into a presidential campaign,” said McGurn.

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He said he thinks Barr needs to appoint a grand jury because, “A grand jury can subpoena. A grand jury can indict. You indict someone at the FBI and we'll get to the story pretty quickly.”

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He added, “Grand juries clarify testimony, clarify the mind and I think one reason we saw such a frenzy when Bill Barr just said ‘I'm going to take a look at this,’ you would have a very different Washington if there is a grand jury and some of these former FBI, DOJ, maybe even CIA officials are brought before it.”