Yarn bombers are trying to negotiate the return of two large knitted "sunshines" stolen from a footbridge.
The perpetrators sent a video of themselves taking the artworks in Cambridge to one of the knitters.
The woolly works had been on the bridge at Jesus Green for two months, as Cambridgeshire Live reported.
Artist Tigerchilli told the BBC: "It really feels like a kidnapping and we're trying to find an anonymous drop-off point for their safe return."
The sunshine motifs were taken on Thursday night - one knitted by Tigerchilli, the other by artist Sophie Neville.
The thieves' film clips disappeared after Miss Neville watched them on Instagram.
"I was shocked when I saw them, and a bit angry that someone would be so mean as to send a video," she said.
"It looked like a group of very drunk people, but it must have taken some time as the sunshines were very securely attached to the railings."
She tried to email the senders and got only one reply.
"It was an unusual Italian email address and the person apologised, said they had been very drunk and wanted to give them back," she said.
"However, they've not been in touch since, so it's a little like the knitting is being held hostage."
Tigerchilli said the collective which made the display of nine sunshines did not report the theft to police as "technically it's illegal graffiti".
However, the bright artworks, which have now all been taken down as anyway planned, have brought joy to many with some leaving "thank you" notes on the bridge and dozens wishing for stolen sunshines' safe return on Facebook posts.
The artists said there would be "no repercussions" for the thieves, and they hoped the sunshines could be returned so they could be displayed again later in the year.