Doomsday Clock #1 introduced two new characters to the Watchemen timeline, Erika Manson, aka the Marionette, and her husband, Marco Maez, aka the Mime.
Doomsday Clock #2 gave us a bit more information about their backstory, as well as revealed their connection to Doctor Manhattan, and why Ozymandias sees them as such a crucial element in his plan to get Doctor Manhattan to return.
The two were a part of a wave of costumed criminals that popped up in response to the rise of the costumed heroes of their world (the Minutemen and the Watchmen.) One day, they decided to carry out a bank heist, which saw the two take the place over by themselves, as well as the Marionette slicing the bank manager's finger off with minimal effort.
Doctor Manhattan soon arrived on the scene, seemingly with the intention of killing the two, but something (implicitly the knowledge of the couple's young son) caused him to stay his hand and allow them to be taken by police instead.
As the new Rorschach pointed out, Manhattan had "eviscerated people for less", which was precisely Ozymandias' point. He knew that the Marionette and the Mime represented a moment in Doctor Manhattan's past in which he showed mercy. Hence, why he believes they may be the key to convincing Manhattan to come back to their world and save it from the approaching nuclear doomsday.