A software developer at Susquehanna International Group (SIG) was arrested by the FBI last Wednesday (12th April 2017) in their offices.
Dmitry Sazonov, age 44, had been an employee for 13 years and appears to have worked on both the general codebase for the trading platform as well as code for actual trading strategies.
The story that the Department of Justice tells seems to be a mixture of spontaneous acts and general silliness:
The developer must have sensed his job was in jeopardy after his supervisor resigned in February. Nervous about his future prospects at the firm, he started researching "steganography" from his work computer (the art and science of hiding data in another set of data... e.g. a file within another file).
He prepared several groups of files for exfiltration, hiding source code within various PDF files and ZIP files.
What is interesting is that he appears to have clearly tipped the company off himself through his own behavior, otherwise SIG might have never become aware of his doings.
A day after his supervisor left (or was let go), Sazonov was going to meet with his new immediate superior and discuss his future at the firm. Having prepared, but not sent, his packaged files, he then found out that he was fired at that meeting and was supposed to be escorted out of the building immediately. Apparently he kept asking to be allowed to go back to his desk, and even once out of the building he kept making phone calls to other employees imploring them to e-mail him the "personal files". It is this insistence that undoubtedly caused people at Susquehanna to take a closer look.
Following a scheduled handover of the supposed files, he was then arrested by the FBI in the lobby of Susquehanna's offices.