The killer is revealed to be Ryan Smulson , the seemingly clumsy and eager police intern.
Season 2, Episode 10 is titled "No Weddings and a Funeral," but it is often discussed in the context of "Love and Death" due to the death of a major character's father.
Analyze Ryan's psychological state. He is a Wesen who wants so desperately to be a "heroic" Grimm that he becomes a monster to his own people. [S2E10] The Hour of Death
Ryan is not actually a Grimm. He is a Lebensauger (a Wesen) who suffers from extreme self-loathing. He obsessed over Grimm history to the point of killing his own kind to "prove" he belonged with the Grimms. Key Themes for a Paper/Analysis
An episode in Season 2 featuring Morgan Freeman discusses experimental models for human death . The killer is revealed to be Ryan Smulson
If you were referring to a different "[S2E10] The Hour of Death," there are a few other possibilities, though Grimm is the most prominent:
An episode in Season 2 titled "Signed in Blood" focuses on handwriting analysis to uncover premeditation in death cases. Grimm season 2 episode 10 review: The Hour Of Death He is a Wesen who wants so desperately
A series of brutal murders targeting the Wesen community in Portland sends them into a panic. The killer leaves behind a symbol—a "G"—that marks a particularly violent and extremist lineage of Grimms known as the Endezeichen .