U.S. Ambassador to the European Union Gordon Sondland returned to Capitol Hill Monday to review the transcript of his testimony to the House impeachment investigators earlier this month, according to two sources familiar with his schedule.

Sondland told lawmakers that President Donald Trump assigned his personal lawyer Rudy Giuliani to carry out Ukraine policy for the U.S. Sondland reportedly said he was not aware that Ukraine policy was in part focused on working with Kyiv officials to investigate 2020 presidential candidate Joe Biden and his son, Hunter.

The ambassador’s presence on the Hill Monday came as a surprise to individuals who work alongside the ambassador overseas. Sondland’s whereabouts have been a bit of a mystery, according to three individuals familiar with his work throughout the European Union.

Last week he skipped a teleconference with other European ambassadors. Two sources said he missed the call because he was traveling. One other person familiar with Sondland’s schedule told The Daily Beast he was still on the job but would not elaborate about the ambassador’s travel. Three sources said he has been out of the Brussels office for more than a week.

The State Department did not respond to repeated requests for comment.

Meanwhile, lawmakers are considering bringing Sondland back in for questioning following last week’s deposition by William Taylor, America’s top diplomat to Ukraine. According to a copy of his remarks, Taylor said Trump told Sondland Ukrainian President Volodymyr Zelensky had to say something in public and “clear things up” about investigating Hunter Biden’s work in the country.

Lawmakers said that Taylor’s account puts the onus on Sondland to come back and clear up inconsistencies or gaps in his initial testimony, during which he frequently said he didn’t recall certain events.

“Generally, it might be a good idea for Mr. Sondland to want to come back,” said Rep. Gerry Connolly (D-VA) after hearing from Taylor, whose appearance last Tuesday most clearly established the quid-pro-quo regarding U.S. security aid and Ukrainian investigation of the Bidens that Trump is denying he sought.

“Obviously you could call everyone back, but I think Mr. Sondland has some more explaining to do,” added Connolly.

Top lawmakers involved in the impeachment inquiry have generally avoided talking about whether Sondland should return for testimony, preferring to focus on the other witnesses who are lined up for depositions in the coming days. A spokesperson for House Intelligence Chairman Adam Schiff (D-CA) declined to comment on whether Sondland would be asked to come back.

But Rep. Eliot Engel (D-NY), who chairs the House Foreign Affairs Committee that is helping to lead the inquiry, did not rule out the possibility last week.

"I think it's too early to comment until we've seen everything, until everybody's testified,” Engel told The Daily Beast. “But I wouldn't be reluctant to call someone back if we felt we needed clarification.”