Mega Buzz: 3XK
Any update on whether Castle will be touching on the 3XK killer again? - Chase
ADAM: The show is definitely keen on revisiting that story line, but it's all about timing. "We're having talks about whether we're bringing him back by the end of this season," executive producer Andrew W. Marlowe says. "But we're still waiting to hear on Season 5. If we get the Season 5 pickup, it's something that we might wait and make more of a meal of next year."
Source
ADAM: The show is definitely keen on revisiting that story line, but it's all about timing. "We're having talks about whether we're bringing him back by the end of this season," executive producer Andrew W. Marlowe says. "But we're still waiting to hear on Season 5. If we get the Season 5 pickup, it's something that we might wait and make more of a meal of next year."
Source