Amid Elon Musk’s legal battle with Twitter, his attorneys have now subpoenaed the company’s former security chief, Peiter “Mudge” Zatko, to appear for a deposition on September 9th. Zatko last week submitted a lengthy whistleblower complaint against Twitter to the Securities and Exchange Commission, the Department of Justice and the Federal Trade Commission. He accused the company of (among other things) having “egregious” security issues. Zatko suggested the problems may pose a national security risk.

In the subpoena, which was filed on Monday and obtained by The Verge, Musk’s attorneys request materials related to how Zatko’s tenure at Twitter ended and what stock, if any, he owns in the company. There are also demands for documents that might indicate any illegal activity by Twitter or foreign intelligence agents it employs. Perhaps most pertinently to Musk’s attempt to back out of his agreement to buy Twitter, the subpoena asks for information connected to the monetizable daily active users (mDAUs) metric Twitter uses, as well as documents Zatko has on Twitter’s alleged spam problem.

Zatko claimed in the complaint that Twitter lied to Musk about the prevalence of bots and spam accounts, as The Washington Post notes. Musk has accused Twitter of fraudulently masking the true number of bots. In his bid to abandon the acquisition, Musk said Twitter made “false and misleading representations” about how many phony accounts are on the platform.

In July, Twitter sued Musk over his attempt to wash his hands of the deal. Musk filed a countersuit later that month. His team has also subpoenaed former Twitter CEO Jack Dorsey. The case will go to trial in October

Meanwhile, Senate and Congressional committee leaders are investigating Zatko’s claims. The whistleblower is set to appear at a Judiciary Committee hearing five days after he’s scheduled to be deposed in Musk’s case against Twitter. Zatko’s assertions have been disputed by Twitter and its CEO Parag Agrawal.