The culprit currently remains a mystery, but it is thought to be a student playing a practical joke. It is also not known how anyone managed to scale the buildings, particularly the spire of Humility, which is thought to be impossible to climb. One suggestion is that the person used the famous book The Night Climbers of Cambridge, originally published in 1937, which offers a guide onto the roofs of the city's ancient buildings.

The Night Climbers of Cambridge is a book written under the pseudonym "Whipplesnaith" about nocturnal climbing on the Colleges and town buildings of Cambridge in the 1930s. "Whipplesnaith" is apparently a pseudonym for Noel Howard Symington, although the book is the work of several contributors. One of them, Eric Wadhams, a choral scholar at King's, either took or was featured in most of the photographs...
The book is now highly sought after, especially in Cambridge itself where it is still regarded as one of few "guidebooks" to the routes onto the roofs of the town's ancient buildings.