Special counsel Robert Mueller has accused Donald Trump’s former campaign chief Paul Manafort of witness tampering. Manafort allegedly tried to hide his communications with potential witnesses using the encrypted messaging apps WhatsApp and Telegram, but prosecutors appear to have accessed the messages via his iCloud account.

Manafort is the highest-profile member of Trump’s team to be indicted by the special counsel, who is investigating Russian meddling in the US election. The court put Manafort under house arrest, on a $10 million bond. Prosecutors say the messages violated the terms of Manafort’s release, which means he might have to go to jail.

The special counsel’s filing to a Washington DC’s district court yesterday included Manafort’s messages, described as “an effort to secure materially false testimony.” Manafort messaged people from The Hapsburg Group, a firm he worked with and funded to lobby for Ukraine’s interests in the United States. According to the filing, he was trying to convince them to lie to investigators about the group’s activities.

WhatsApp has a setting that automatically backs up messages to iCloud. If enabled, this would render the app’s famous end-to-end encryption useless in terms of hiding from law enforcement equipped with a search warrant. The prosecutors also had statements and documents from the two potential witnesses, as well as phone records, but the iCloud account helped them confirm the messages and phone calls that Manafort had attempted. The US government routinely requests information from internet companies through warrants and subpoenas.