Suicide

When a note connected to a supposed suicide is found, the team re-opens the 1994 case of a high-school kid who fell from the roof of the school building after having served detention. In 1994 the death was deemed a suicide, but the newly-found note indicates that the victim might have been fearing for his life.

Goodbye forever bloody / but beautiful we three are / falling from heaven

In the fourth season finale, a hostage situation arises when the entire team is held captive while they're investigating the 2006 killings of a family who had just moved into a new house.

The team re-opens the case of a woman who allegedly committed suicide in 1962 when the victim's granddaughter comes forth with evidence that the note found on the death scene -- then thought to be the suicide note -- was not written in the victim's handwriting.
She was a beautiful woman. Full of life. Until she started slipping.

Hollow. No escape from the dark. I sit. Alone in empty rooms.

The team searches for the killer of Luke Cronin, a champion debater from humble means who was wrongly believed to have committed suicide after losing his first debate three months into his scholarship-funded schooling at a competitive top private high school.

The only one who can judge you is you. (...) I judged myself today, like you said, and I didn't like what I saw.

I am my own evidence.