A mysterious sealed document in Michael Cohen’s criminal case was referenced in the online court docket in federal court Wednesday.

The docket entry notes only that the sealed document was “placed in vault” with the Southern District of New York in Manhattan. There is no information on what type of document it is, or even the word count. It’s not even clear if it’s just a clerical note referencing an action involving a previously sealed document, or a new document being filed in the case.

Asked for more information, SDNY spokesperson Jordan Prince said: “That’s all that’s really available. I’m not sure if its an entry, if it’s a filing. It just indicates that there’s a sealed filing placed in vault.”

The new docket entry arrives a week after Cohen was sentenced to three years in prison for financial crimes including tax evasion and making hush money payments on President Trump’s behalf in a case brought by the Manhattan U.S. Attorney’s office. Cohen also pleaded guilty to lying to Congress in a separate case brought by special counsel Robert Mueller.

The former personal attorney to the President went to “significant lengths” to cooperate with the Mueller probe, according to prosecutors on that team. Cohen has offered to continue providing information to the special counsel and federal prosecutors in New York now that his sentencing is complete.

He is set to surrender himself to federal custody on March 6.