Whistleblower documents show that Joe Biden was “aware of Hunter Biden’s business arrangements and may have been involved in some of them,” according to Republican Sen. Check Grassley, which could suggest that the FBI has “voluminous evidence” about the case.

Grassley sent a letter on Monday to Attorney General Merrick Garland, US Attorney for Delaware David Weiss, and FBI Director Chris Wray.

Grassley claims that the FBI has documents in its possession that contain information related to Ukrainian natural gas firm Burisma Holdings.

“The documents in the FBI’s possession include specific details with respect to conversations by non-government individuals relevant to potential criminal conduct by Hunter Biden,” wrote Grassley.

“These documents also indicate that Joe Biden was aware of Hunter Biden’s business arrangements and may have been involved in some of them,” Grassley said, noting that it is “unclear whether the FBI followed normal investigative procedure to determine the truth and accuracy of the information or shut down investigative activity based on improper disinformation claims in advance of the 2020 election.”

“It is also unclear whether U.S. Attorney Weiss has performed his own due diligence on these and related allegations,” Grassley wrote.

Fox News reports “Grassley and Sen. Ron Johnson, R-Wis., led an investigation into Hunter Biden beginning in 2019 and found that Obama administration officials ‘knew’ that Hunter Biden’s position on the board of Burisma was “problematic” and that it interfered ‘in the efficient execution of policy with respect to Ukraine.'”

The younger Biden joined Burisma in 2014 and connected the firm with Blue Star Strategies. The connection was made to help the company fight corruption charges in Ukraine.

“After Joe Biden left the vice presidency, the summary makes clear that Hunter Biden and James Biden worked with CEFC and affiliated individuals to compensate them for that past work and benefits they procured for CEFC,” Grassley wrote, referring to CEFC China Energy.