Washington (CNN) Investigators from special counsel Robert Mueller's team briefly questioned Maria Butina in January, but she did not appear to be central to their investigation into Russian meddling in the 2016 election, according to two sources familiar with the matter.

Mueller's team questioned her on only one occasion for approximately an hour, sources said. The vast majority of Butina's cooperation has been focused on the case the US Attorney's office in Washington, DC, has been building against Butina's boyfriend, Paul Erickson.

"Maria's plea agreement requires cooperation with any relevant entities," said Robert Driscoll, Butina's attorney. "She's complied with all such requests."

The special counsel's office was interested in Butina's interactions with J.D. Gordon, a former national security aide on the Trump campaign, two sources said. Investigators also questioned Butina about whether she had any insight into the Trump campaign's effort in July 2016 to change language in the Republican National Committee platform about Russia's aggressive moves in Ukraine.

Gordon was also questioned as part of Mueller's probe but was not accused of any criminal wrongdoing.

A spokesman for the special counsel declined to comment.

Butina's encounters with Gordon came months after the platform changes that attracted Mueller's attention. She and Gordon were in touch in September and October of 2016 and the two of them attended a Styx concert together.

Mueller's team appeared to interview Butina as a formality, sources said. The special counsel's team interviewed roughly 500 witnesses over the course of its two-year investigation, which came to a close last week, according to Attorney General William Barr's summary of the probe.

A 30-year-old Russian national, Butina pleaded guilty last year to trying to infiltrate GOP political circles and influence US relations with Russia before and after the 2016 presidential election. A sentencing date has not yet been set.