Leaked emails written by senior Leighton Holdings' staff in August reveal that insiders from Visionstream were suspected of assisting the Silcar staff steal tender files relating to an Optus mobile network contract the two firms were ostensibly fighting each other to win. Visionstream is owned by Leighton Contractors while Silcar was half owned by Leighton firm Thiess at the time of the corruption. Since July, it has been fully owned by Thiess. The revelations of corruption inside its two Australian firms comes as Leighton Holdings remains under scrutiny over its handling of allegations of serious corruption and bribery in its international operations. Fairfax Media can also reveal that the international scandal has prompted the fourth resignation of a top executive. The Dubai-based Habtoor Leighton Group chairman Riad Al Sadik has confirmed he has resigned from a company founded by Leighton's former international boss, David Savage. Mr Al Sadik's resignation from Stonehouse comes after revelations in Fairfax Media that Mr Savage secretly formed Stonehouse while still working for Leighton Holdings, despite the potential for Stonehouse to compete with the Australian construction company. The revelations about Leighton's domestic troubles raise fresh questions about the company's culture and operations, which have for years involved separate and competing subsidiaries vying with each other to win major projects.

Leighton recently sacked several of the employees of Visionstream and Silcar - including three managers and two other employees - implicated in the scandal, which until now has remained hidden from shareholders and the public. In a statement sent to Fairfax Media on Thursday, Leighton Holdings said that after an audit, "Visionstream and Silcar separately conducted further investigations and … immediately stood down staff apparently involved. Silcar withdrew from the [Optus] bid process." While both Silcar and Visionstream are ultimately owned by Leighton Holdings, they are regarded by the construction and infrastructure group as separate and competing firms. The detection of fresh corruption in the subsidiaries' ranks sparked major concerns among Leighton Holdings' top lawyers. Leaked documents show that in August, Leighton authorised a secret internal inquiry involving the checking of emails and phone records. In one email, dated August 23, Leighton Holdings' senior counsel, Michael Charlton, stated that an internal investigation had uncovered emails "off the Silcar system" which is in fact "the information of Visionstream". Other emails show that top Silcar managers were emailing each other about the stolen and leaked information relating to the rival Visionstream contract bid.

"Shit, how many people did they have working on this?" one Silcar executive wrote, after being leaked inside information from the secret Visionstream bid. In another email, an allegedly corrupt executive emails his colleague requesting leaked information. "What was VPL's [Visionstream's] round 2 final offer value?" one manager emailed his colleague. "$322 million," the colleague responded. In a statement, Leighton Holdings also defended its decision not to notify authorities, including police or the Australian Competition and Consumer Commission about the scandal, despite the conduct of the sacked staff potentially breaching anti-collusion or criminal laws. "Visionstream and Silcar each separately determined that there was no collusion and that it was not a matter that required referral to the ACCC.

Loading "Leighton Holdings condemns any form of illegal behaviour and, in the event that any individuals associated with Leighton Holdings behave improperly, we take appropriate action. In this case, the employment of the individuals was terminated." Visionstream won the $240 million Optus contract after Leighton Holdings discovered the illegal activity.