Rick Gates, the former official for President Donald Trump‘s election campaign, had contact with someone associated with Russian intelligence during 2016, according to new court filings by Special Counsel Robert Mueller.

The filings described an associate of Gates—believed to be Konstantin Kilimnik, according to several reports—known as “Person A,” and added that Gates was aware of his links to “Russian intelligence service.”

Kilimnik reportedly worked with Paul Manafort in Ukraine and his possible ties to Russian intelligence have been reported by numerous media outlets. He has denied being involved with Russian intelligence.

Gates and Manafort were indicted on money laundering and other charges by Mueller last year. Gates pled guilty earlier this year and is believed to be assisting Mueller’s investigation.

The discussions between Gates and “Person A” came from court documents regarding Alexander van der Zwann, who was charged as part of Mueller’s probe in February. He pled guilty to lying to investigators about his interactions with Gates.

Recently, Trump has reportedly voiced his frustration with Mueller’s investigation, telling confidants that he thinks the probe is “going to choke the life out” of his presidency.

You can read more about the latest court filings here.