Two former Twitter employees have been charged with spying after they reportedly obtained personal account information for critics of the government of Saudi Arabia.

A complaint unsealed on Wednesday in US district court in San Francisco detailed a coordinated effort by Saudi officials to recruit employees at the social media giant to look up the private data of thousands of Twitter accounts.

One of the former Twitter employees, Ahmad Abouammo, was arrested on Tuesday on charges of spying and falsifying an invoice to obstruct an FBI investigation. He is a US citizen. The other former employee, a Saudi citizen named Ali Alzabarah, was accused of accessing the personal information of more than 6,000 Twitter accounts in 2015 on behalf of Saudi Arabia.

Alzabarah accessed accounts of a number of prominent government critics including that of Omar Abdulaziz, a prominent journalist with more than 1 million followers who was close to late Washington Post columnist Jamal Khashoggi. Khashoggi, a US resident, was killed by the Saudi government last year.

The US justice department also alleged that the employees – whose jobs did not require access to Twitter users’ private information – were rewarded with a designer watch and tens of thousands of dollars funneled into secret bank accounts.

Alzabarah allegedly admitted to his supervisors that he accessed user data and said he did it out of curiosity. He was placed on administrative leave, his work-owned laptop was seized, and he was escorted out of the office.

The next day, he flew to Saudi Arabia with his wife and daughter and has not returned to the United States, investigators said. A warrant for his arrest was issued as part of the complaint.

In a statement, Twitter thanked the FBI and the US Department of Justice for supporting the investigation.

“We recognize the lengths bad actors will go to try and undermine our service,” Twitter said. “We understand the incredible risks faced by many who use Twitter to share their perspectives with the world and to hold those in power accountable.”