Drunken numpty
I read this report in quite a different way from others
"The Met told us they were called to the institute on January 23 at approximately 2025 UTC to "reports that a man had entered the British Museum and caused damage to the museum's security and IT systems."
I don't think he has used ninja-knowledge, I think he has gotten liquored up after his last hour at work, forced his way back in, in so doing he has set off RedCare or equivalent.
The plod have arrived, probably struggled to get in at first, maybe went to see if some jewels had been liberated and finally found our hero in the server room where he had smashed up some equipment and/or disabled some systems at a basic level.
Exhibitions need to remain closed thereafter until the relevant equipment can be replaced/repowered in order that said jewels above can remain secure.
50 year old contractor - how/why had he been dismissed? Has his temperament done him down twice?