A bit about Murder Mystery Games – courtesy of Wiki.
Murder mystery games are generally party games wherein one of the party-goers is secretly, and unknowingly, playing a murderer, and the other attendees must determine who among them is the criminal. This may involve the actual ‘murders’ of guests throughout the game, or may open with a ‘death’ and have the rest of the time devoted to investigation.
Murder mystery games may also refer to public performances in venues for events, team building or corporate entertainment, where the suspects are played by actors, and the role of detectives falls to the other guests.
Dinner party murder mystery games are generally played with small groups of individuals, e.g. 6-20. Murder mystery events for larger groups are usually run for numbers between 20 and 250 attendees, though events can be run with 400+ in attendance.
The Origin of The Murder Mystery
The murder mystery genre began in the first half of the nineteenth century.
1935 saw the release of the first murder mystery game known as jury box,  which differs significantly from modern murder mystery games. In jury box the players or jurors are given the scenario of the murder, the evidence presented by the prosecutor and defendant, two photographs of the crime scene and ballot papers. Jurors have to make the decision as to who is guilty and then a real solution is read out.
Cluedo or ‘Clue’ in North America, the first murder mystery board game was released some time later in 1948, and has continued to be popular. However, Cluedo is again, a vastly different game to the modern role playing dinner party mysteries.
The earliest mention of role playing murder mystery games in their present boxed format is in the 1980s when they were thought to be a bit of a one-year wonder in the game shops. Back then the scenarios were simple, the acting directions minimal, and the games relied on the guests being comfortable ad-libbing responses to each other’s questions.
In the last 20 years those basic games have increased in complexity into the more complex role playing dinner party games available today.
Dinner party games
Murder mystery games for dinner parties are often structured so that each guest is equally involved and designed to be played in the host’s home, using boxed games or internet downloads.
Dinner party kits can take the form of structured games or freeform games. Structured kits are the style more commonly available to purchase, and suit a wide audience. Freeform mysteries are better suited to experienced role players who are confident ad-libbing and who show initiative.
In structured mysteries the participants are told exactly what to say and when. They are often provided with introductory statements, questions to ask, answers to give and occasionally some shared dialogue to break the ice. Character information often comes in booklets which are read from throughout the course of the evening.
In freeform games the guests are provided with character backgrounds and they are given license to interrogate or perform actions or activities with the other guests which will help them solve the case. 
The games for 6 to 20 players are usually played over 2–3 hours and the players use their character booklets and clues (i.e., the game contents) to delve into the background of the murder using the questions, answers, hints and clues provided. These are all designed to elicit more and more information about the murder, until the players are in a good position to suggest who they believe is the guilty party.
More often than not, players will be invited (by the host) to attend the party dressed as, and ready to play the part of, one of the suspects listed in the game scenario. The game is usually played over a 3 course dinner party, although freeform games can often be played as a mix and mingle style format.
Boxed or downloadable games are designed to be played by groups of friends or family, who are seeking to enjoy a fancy dress style party with an additional ‘theme’. The setup of these games can be simple or elaborate. Some games require no setup beyond a way to randomly select the roles; however, some party hosts like to develop an elaborate menu and decorate extensively.
As well as providing the food and drink for the evening, the party host is required to follow the simple instructions, prepare for the party in advance, and generally co-ordinate proceedings during the evening. Organizers of the mystery can select roles and characters based on their knowledge of the guests.
Some of the boxed or downloadable games are designed so that they can actually be solved by the players, using the clues provided, whilst others can’t and are played just as a form of light entertainment. Players are usually required to act as one of the characters/suspects involved in the plot, and must ask and reply to questions using the information provided in their character booklets and on clue sheets.
Large group murder mystery game
As not everyone can take a role in a large group game, the suspect roles are usually given to actors, who learn scripts or just add lib a performance which will gradually reveal who the murderer is to the other guests. The actors are fully “in the know” about all aspects of the case.
The remaining guests will take on the role of detective and it will be their “job” to actively solve the case by examining evidence, finding clues, following and questioning suspects – whatever it takes for them to solve the mystery.
Large group events can be run in several ways including:
In a single room with a staged theatrical performance,
With actors acting “in the round” amongst the guests,
In multiple rooms with clues scattered throughout the venue and suspects in different areas.
As more traditional card games with clue cards given to the guests with chunks of information on each one.
In video format with evidence being presented to teams after watching suspect videos.
In a combination of script and clue evidence.
Large group games are often played in a hired venue, a restaurant, a hotel, or at a workplace. They are often used for fundraisers, team building and corporate events.
(*Live versions of murder mystery shows, in which guests attend commercial venues such as hotels as paying viewers, are sometimes classed as dinner theater or mystery dinners, not Murder Mystery Games.)
Murder Mystery Games come in several different versions:
Structured or turn-based games work by releasing information over the course of the game. As the game progresses, each character learns something new about the plot and their involvement. Each turn players are prompted to ask specific questions, or perhaps read from a script. These are popularly played around the table at a dinner party. and then there were none.
Freeform murder mystery games provide players with details of their character from the start, but it is up to the character to determine how they solve the murder. Often players have other objectives – such as to be the richest player at the end of the game. Most people will have their own secrets that have nothing to do with the murder. This provides even more reasons for players to interact with each other. These games are better suited to buffets or finger food as generally everyone needs to be able to mingle and also to talk to others without being overheard. Some are done during a sit down dinner as long as time is provided afterwards for guests to move about and mingle.(The drawbacks of this style is that when the murderer is revealed at the end, often guests feel cheated that they were not privy to the same secret information some actor quietly revealed to other players.) There are a variety of different styles of freeform games available; some encourage interaction prior to the event itself with alliances forming in advance of the evening, and a more “court” style approach on the actual night where everyone has to vote who committed the act.
Scripted mysteries will have 5 to 10 detailed characters as suspects (usually played by actors, or more confident guests), each with a detailed background and story. Everyone else plays detectives trying to solve the murder. These games require the detectives to interrogate the suspects to determine the holes in their story, and are clearly focused on solving the murder.
Video based or on-line interactive mystery games will use video to provide the back story to the crime and may provide witness testimonials or show evidence to allow guests to solve the case in a more “game” style format. These are often played individually on the internet, but sometimes are played in larger groups for team building.
Murder mysteries can be played on internet forums, the organizer privately notifies the murderer to let them know and they must try to blame someone else on the thread. At the end of a round, the organizer reveals the murderer.
Variants may involve changing the nature of the crime (especially if younger players are involved), allowing some participants to know certain facts in advance (even the identity of the murderer), or having ‘plot twists’ of unexpected events to occur, to help or hinder the investigation, as needed. Games aimed at younger children may contain puzzles and problems to solve or scripts.
Wiki link to this article: https://en.wikipedia.org/wiki/Murder_mystery_game
- Making freeform murder mysteries – http://www.youandmegames.co.uk/how-to-make-murder-mystery-party
Summerscale, Kate (2008). The Suspicions of Mr Whicher, Or the murder at Road Hill House. Bloomsbury. ISBN 978-0-7475-8215-1.