When Chloe O'Brian found a syringe in Jack Bauer's office trash bin, she called a lab technician to come and test it. Using a drug kit, Jesse confirmed that the syringe tested positive for opiates, proving that Jack was using heroin.
Steve Lanza re-appeared during Seasons 4, 5, and 6, but in Season 4 he was addressed by Tony Almeida as "Danny". For the purposes of this project, Jesse and Danny are treated as two distinct characters. Despite the different names, both characters did similar tasks such as analyst work and medical technician functions.