An investigation was launched after thousands of pounds of damage was caused to a Liverpool cultural landmark.
Vandals attacked the John Lennon wrap covering St George's Hall.
They scaled scaffolding behind it before scoring out a circle from the left lens of Lennon's spectacles.
The poster was paid for by the North West Development Agency to cover the hall while it is renovated.
It took 30 gallons of ink and 150 hours to print and depicts ex-Beatle Lennon as the Mona Lisa with a guitar.
The wrap gained international exposure, being seen by millions around the world as Liverpool's campaign to become European Capital of Culture.
Today Liverpool city council launched an investigation into the attack but a construction worker at the site said: "No-one knows who did it.
"I have heard a few people say it must have been one of us so that we can look into the student accommodation opposite, but you'd need pretty powerful eyesight to do that.
"There's no way anyone could bring a telescope or binoculars on site because security is so tight.
"If anyone really wanted to look into the halls you wouldn't need to cut a hole because there are plenty of spaces along the scaffolding where you can see out.
"Whoever did it certainly knew what they were doing. The hole is cut perfectly."
A council spokesman said: "We have also been in touch with the NWDA and they are looking at ways of repairing it."
A spokeswoman for Merseyside police said: "We have not received a complaint as yet."