Danny was born into the times where it was almost necessary to be a member of a gang. his older brother louie is a member of the notorious gang "tanglewood". br>
He was born as Daniel Messer. Danny grew up on Staten Island in an "Italian Mafia" family under surveillance (as hinted at in the episode "Tanglewood"), he formed his own set of hybrid ethics, caught between the world of lawbreakers and lawmakers. Mac personally selected Danny for his team, an honor and a responsibility that he attempts to live up to each day. His relationship with Mac is severely tested when Danny goes to Internal Affairs behind Mac's back ("On the Job") and almost loses his job, although he ends up being merely removed from the promotion grid and demoted to CSI second class. br>
He is a very suspicious person; though he gets along well with the rest of the CSI team, Flack is one of the few people he truly confides in. Danny attended college and played minor league baseball until he got into a bar fight and broke his wrist, after which he went to the police academy and graduated first in his class ("The Closer"). Almost a year after the original Tanglewood case, Danny is implicated in a 15 year-old cold case. His older brother Louie, a Tanglewood gang member, is severely beaten by the gang and left in a coma, although he manages to get a taped confession from the real killer which clears Danny of the charge with the help of Mac. Danny also has a budding relationship with Lindsay, whom he affectionately calls "Montana"..