[X] Theory- Masuda's identity was stolen at some point prior to the final entry. The man who was notably standoffish and not particularly notable was replaced, somehow, by the identity thief- who took advantage of Masuda's background and his own, apparently significant, degree of technical skill in order to gain a Magenta clearance. You're not sure what his precise motivations are, but he- and the other runners- wanted access to the information they took from the site. In order to access that information, they used 'Masuda' as an inside man while they planned their heist. Something went wrong, though- if nothing went wrong, you'd have never heard about the heist, because nobody would know about it. Either the guards caught 'Masuda' and his comrade talking, and had to be eliminated (with backup being called in), or the other runner was trying to take advantage of the heist to gather information of their own, and 'Masuda' took advantage of being the inside man to get the upper hand when he caught her. Either way, after things went wrong more runners showed up in order to collect the information and help cover 'Masuda's' tracks. You're still missing information you'd need to know exactly what happened and why, though- why did the Shadowrunners want an archeologist's notes?