While Law & Order: SVU began as a spinoff, it has become the most successful of the Law & Order franchise. The series has seen a lot of cast members come and go, and the format has gone through some changes. One of those changes, however, is not how the show utilizes suspect lineups.

The show uses lineups when there are survivors of attacks in order to see if the survivor can identify the suspect the police have in custody. They are not unlike suspect lineups used in the real world, but there is one detail in the SVU lineups that is easy to overlook at first.

SVU Has Used Three Different Types Of Suspect Lineups Over The Years

SVU Uses Photo Arrays, Sequential Photos, And Physical Lineups

Law & Order: SVU has been using lineups in various forms since the first season of the show. The early seasons liked to employ photo arrays when questioning witnesses outside the precinct. This meant that several mugshots were on a single piece of paper, and that paper was given to a witness.

Over time, the series addressed the idea that photo arrays like that, in which a suspect is confronted with several different images at once, were less likely to get a correct response. When an SVU assistant district attorney explained that to the detectives in the show, they began using sequential photos instead.

That meant detectives would provide a witness with one photo at a time and see if the witness recognized each photo. While it’s more likely to get an accurate response, it’s not the most common type of suspect lineup presented in SVU. That honor belongs to the physical lineup.

SVU’s physical suspect lineups are not unlike those presented in any other police procedural. A group of suspects files into a room holding a number while the witness, detectives, and lawyers stand in an observation room with one-way glass. Each person is asked to step forward, or to say something a survivor heard during an attack, or both.

The witness or survivor is then asked if they recognized anyone in the lineup. Each person in the lineup has a number rather than a name, so the survivor does not know anything about them.

Only one of the people in the lineup is actually the suspect in custody. The rest are either police officers in plainclothes who have a similar appearance to the suspect or individuals who have been paid a fee to stand in the lineup.

Just how the detectives make it clear that the witness is done is a detail that has remained the same since the start of Law & Order: SVU.

SVU Detectives Identify The Suspect By Rapping On The Observation Window

The Number Of Knocks Is The ID Number

Since SVU started using physical lineups in the first season of the show, the detectives in the room with the witness have a unique way of making the witness’s identification of the person in the lineup clear.

After the witness gives the number to identify the person they recognize, the detective in the room raps on the glass to let the officer who led the lineup into the room know that the person has made an identification. In the early seasons of the show, it simply looks like a signal that they are done. That’s not the case.

The number of times the detective hits the window is actually the same number as the identity named by the witness. It seems obvious in later seasons of the show when the detective is hitting the window five or six times, but in the early seasons, it was much less so, making it easier for the audience to miss.

In the early seasons, the suspect was often placed in the 2, 3, or 4 position, so the rhythm of knocking on the glass seemed natural. It’s a lot less natural to have someone knock on the glass five or six times, making the pattern easier to see – especially if you binge-watch a long stretch of the show in a rewatch.

I only caught this particular detail on a rewatch of the series 12 seasons in, when Elliot Stabler (Christopher Meloni) knocked on the glass six times to identify #6, and it only makes SVU feel more authentic. While there have been a lot of soap-opera-like drama and continuity issues when it comes to the timeline, this detail remains the same.

It’s something that seems so obvious in hindsight – how else would the officer in the other room know the outcome without leaving the suspects – and once the detail is noticed, it’s never missed again.

It is a great way for the audience to feel like they’ve got a behind-the-scenes look at just how the investigation works, and it is a great reminder that Law & Order: Special Victims Unit has put a lot of care into how they present their cases to the audience.