Police say there were no signs of forced entry, and that nothing in the home had been disturbed or stolen. Authorities are still investigating the alleged break-in, as the "X-Men" actress says the children's book doesn't belong there.
Janssen, 47, claims no one else had access to her Greenwich Village penthouse, yet a copy of "The Lonely Doll" appeared in her bedroom.
The children's book tells the story of a lonely doll who is befriended by two bears who promise to always be there for her.
If there was a break-in, it wouldn't be the first stalker the Dutch-born actress has fended off. In 2005 Janssen had to file a harassment report with police over a persistent super-fan who sent her menacing letters and photos.
Janssen most recently played Jean Grey in "Wolverine," though she has not confirmed whether she will appear in the upcoming "X-Men: Days of Future Past," to which co-stars Patrick Stewart, Ian McKellen and Halle Berry have already signed on.