Cheeky Squirrel Monkeys!

Squirrel Monkey troop escapes London Zoo

"The squirrel monkeys have managed to gain access to some of the taller trees in their enclosure and from there, have leapt into the higher branches of a tree in Regents Park," a London Zoo spokeswoman said.

They go on to say that the squirrel monkeys pose no threat, but then they mention this bit:

She said they were a very intelligent set of monkeys and staff had previously had to train them to stop stealing visitor's mobile phones.

Thievery and jailbreaking?! These critters are obviously immune to rehabilitation.

Update: As expected, Betty, the last of the bunch to still be roaming around, finally came back on her own.