Season 4

The team head to Canada to investigate the disappearances of a number of homeless people, drug users and sex workers and uncover something horrific in part two of the season finale.

The team head to Canada to investigate the disappearances of a number of homeless people, drug users and sex workers and uncover something horrific.

The BAU co-work with the U.S. Army to find the perpetrator behind an anthrax attack on a park in Annapolis, Maryland.

A serial killer in Bend, Oregon is deliberately killing people by running them over with his car.

The team tracks down a highly obsessive-compulsive killer who targets blonde women and leaves messages to the police asking them to stop him.

An AMBER alert is activated for a young boy in Cherry Hill, New Jersey and the BAU suspect it to be the work of a pedophile who has abducted and killed two other boys.

Male college students on spring break are being raped and murdered, presumably by a man and a woman working together. The BAU are called in and suspect a shy hotel cleaner and a receptionist.

When the kill count of a mass-murdering arsonist active in a small town reaches 31, the BAU are called in.

After being inactive for 10 years, Hotch's first BAU case, an elusive serial killer known as the Reaper, starts killing again.

Prentiss learns from an old friend, John Cooley, that their mutual friend, Matthew Benton, just died from a heart attack. Prentiss had not seen either man in several years, both for different reasons. John also mentions that Matthew thought he was going to be killed just like "Tommy V." In searching, Garcia does find someone matching that name in the area who recently died from dehydration. There are similarities between the two deaths but no medical rationale for tying the two together as murders. A third person in the area then dies in a similar way but again no medical indication of an unnatural death or rationale tying the death to the first two. However, Prentiss and Rossi, in particular within the team, are certain the three deaths are related and that they are indeed murders. They have to tread lightly and carefully since the families of the deceased refuse to speak to the FBI - especially Matthew's family who know, and do not like, Prentiss - and since there is no official case as the police have not sanctioned one. The investigation gets more complicated for the team when they find who they believe is the murderer.

A high priced call girl that is killing her clients must be found and stopped.

A copycat serial killer is recreating murder techniques used by famous killers from the past.

A serial killer in the Olympia, Washington area has abducted four blonde, twenty-something women. When the third victim is found embalmed, the BAU are called in and suspect that the embalming is a way for him to spend more time with them.

A family consisting of two parents and their son break into a home, kill the parents and kidnap their daughter. As the investigation proceeds, the BAU team begin to suspect that what they're dealing with is bigger than they thought.

The team suspects that a member of an affluent community is responsible for the disappearance of a young woman.

A serial killer known as the Road Warrior is gunning down blonde women on roads in Orange County, California and the BAU suspect that the victims are surrogates and that it's only a matter of time before he kills the real one.

Morgan, an ex-cop, takes it personally when a serial killer targets police officers in Phoenix, Arizona.

A greatly sadistic serial killer who disembowels women and forces them to clean it up before killing them proves difficult to catch thanks to his social charm and simple, yet clever, disguises.

A serial killer turns himself in and challenges the team to find five people he has hidden somewhere before they die.

Driven by his nightmares, Reid stays behind in Las Vegas to find his father in order to find out the truth about Riley Jenkins' murder.

A child abduction case in Las Vegas causes Reid to have strange nightmares which appear to be connected to an event in his past.

A man is jumping trains along Highway 99, brutally killing couples in their homes whenever he stops.

A serial killer targeting couples stages their bodies in a way to make their deaths look like car accidents.

Reid and Prentiss, having gone undercover into an underground cult to investigate child abuse, get trapped inside the compound when a state raid on it goes bad.

On the anniversary of a serial killer's execution, a murder spree which appears to be connected to him begins and the team must try and understand his mind in order to stop it.

As the city is on high alert, the team begins to believe that they have made a mistake with the profile and that everything the terrorists have done so far may in fact just have been diversion for something even bigger.