Elon Musk's legal team sent a letter to Twitter Monday saying he now has more reasons for why he can abandon his $44 billion proposal to purchase the social platform.

The letter was published in a Securities and Exchange Commission filing, and cited the recent whistleblower disclosure from former head of Twitter cybersecurity Peiter Zatko, also known by his hacker name "Mudge."

Zatko filed a wide-ranging whistleblower complaint against Twitter in July which became public last week.

Musk first announced his intention to ditch his deal to buy Twitter on July 8, arguing the platform had more bot accounts on it than Twitter had previously disclosed.

Twitter sued Musk in response, accusing him of using his professed concern about bots as a smokescreen, and that his real reason for abandoning the deal was because his personal wealth had plummeted.

Musk's lawyer said in a letter sent to Twitter's chief legal officer that Musk was now serving the firm with a second "notice of termination," adding accusations in Zatko's whistleblower disclosure as reasons why he can legitimately walk away from the deal.

The letter said Zatko's complaint "alleges far-reaching misconduct at Twitter — all of which was disclosed to Twitter's directors and senior executives, including (CEO) Parag Agrawal — that is likely to have severe consequences for Twitter's business."

"These allegations, if true, demonstrate that Twitter has breached the following provisions of the Merger Agreement, thereby giving the Musk Parties the right to terminate the Merger Agreement," the letter added.

Musk's lawyer said in the letter the new termination notice was being filed in case Musk's original case concerning bots was "determined to be invalid for any reason."

Zatko's lawyers confirmed Monday Musk's legal team had subpoenaed Zatko, who is due to be deposed on September 9.