<Tr> <Td_colspan="7"> The Ice Truck Killer strikes again, leaving a real nightmare before Christmas at Santa's Cottage . Sergeant Doakes becomes more suspicious about Dexter after his ambivalence about Batista's survival . Dexter finally finds he is connected to the Ice Truck Killer over a past case involving Harry Morgan and a blood - bath crime scene in 1973 involving Dexter's biological mother . Lieutenant Maria LaGuerta braces herself as Captain Matthews blames her for the department's failure to find the Ice Truck Killer and he has her replaced . Rudy and Debra spend some quality time together, and Rudy proposes marriage to the smitten detective . Rita decides to take her children, Astor and Cody, to visit Paul, who has been sent back to prison . </Td> </Tr> <Tr> <Th> 12 </Th> <Td> 12 </Td> <Td> "Born Free" </Td> <Td> Michael Cuesta </Td> <Td> Daniel Cerone and Melissa Rosenberg </Td> <Td> December 17, 2006 (2006 - 12 - 17) </Td> <Td> 1.20 </Td> </Tr> <Tr> <Td_colspan="7"> Doakes and LaGuerta begin to suspect that Rudy is the Ice Truck Killer, while Dexter finds a suspicious picture of the shipping container where his mother was killed . Doakes begins tailing Dexter, convinced that he is somehow connected to the Ice Truck Killer . A call from her ex-husband makes Rita suspicious of Dexter and his behavior . LaGuerta's replacement, Lt. Esme Pascal (Judith Scott) arrives and takes over the Ice Truck Killer investigation . Dexter recalls that Rudy is in fact his biological brother, whose real name is Brian Moser . Brian intends to kill Debra with Dexter in a reunion with his true family, but Dexter stops him . As the police close in, Brian escapes and Dexter is left with Debra, appearing to have saved her . The same night, Brian breaks into Dexter's apartment and attempts to stab Debra, but Dexter captures him . After an emotionally charged conversation, Dexter slices his brother's throat and leaves him upside down to drain, staging it as a suicide, while wondering what would happen if everyone knew the truth about him . </Td> </Tr>

When do they find out rudy is the ice truck killer