Miami Metro didn’t really uncover Trinity’s identity first — Dexter did , by following leads from Lundy’s investigation and then seeing Trinity in the act. Dexter learns Trinity is Arthur Mitchell, a family man and church deacon, after tracking him and connecting the pattern to his real life.

What happened

  • Lundy’s work narrowed the killer down, and Dexter got access to that information.
  • Dexter then followed Trinity and caught him killing another victim, which confirmed he had the right man.
  • After that, he discovered Trinity’s ordinary family life and his real name, Arthur Mitchell.

Why it matters

Miami Metro’s knowledge came later, through the investigation, but the key reveal in the story is really Dexter figuring it out first. Trinity’s double life is what made him so hard to catch.

In one line

Dexter identified Trinity as Arthur Mitchell by using Lundy’s notes and then seeing him commit a murder.

TL;DR: Dexter, not Miami Metro, is the one who figures out Trinity’s identity first.