Monica West is a disgraced former Assistant Florida State Attorney who was responsible for planting Natalia Boa Vista as a mole within the MDPD's Crime Lab, hoping she would come up with evidence of corruption within the lab.
However, when Natalia only brought back positive results on the lab, West got frustrated enough that she stole some money that the team seized in a raid on the Mala Noche gang.
When her fiancee, Treasury Agent Peter Elliot, was looking over the money, she tipped off the FBI causing the lab to be investigated.
When Ryan Wolfe pointed out that the money wasn't taken from their lab, Calleigh figured it out and had Elliott confess to dereliction of duty.
Calleigh made him get Monica to admit on tape that she was the one who took the money.
She was then arrested and it's presumed that as a result of that, she was disbarred from practicing, lost her job and was sent to prison.
She was played by Bellamy Young.
Snide and arrogant, Monica believes the Miami-Dade Crime Lab is an area full of corruption and as such, will stop at nothing in shutting in down for good, even if it means jeopardising their reputation.
She is very hostile to the employees, especially Horatio Caine and Eric Delko whom she believes are covering for one another or going out of their way to make sure that the truth doesn't come to light.
However, those two traits along with her impatience and need for results ended up proving to be her own downfall.