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One of the most difficult parts of a trial, especially in front of a jury, is accurately describing the crime scene.

A number of courtrooms have begun projecting 3D images of scenes onto walls - but these can only reveal a limited amount of information.

To take criminal courtroom reconstructions to the next level, experts have created a 3D immersive system that virtually transports people inside the scene using an Oculus Rift headset.

The setup uses an Oculus Rift headset (d), the OptiTrack optical tracker (e), laser scanner from Geomagic and Autodesk 3DS Max software to create the final reconstructions. The computer system is shown at (a), (b) is the Oculus USB connector, and (c) is a wall-mounted tracker

It has been dubbed 'forensic holodeck' after the environment simulator used in sci-fi show Star Trek.

The low-cost setup uses an Oculus Rift headset, the OptiTrack optical tracker, a laser scanner from Geomagic and Autodesk 3DS Max software to create the final reconstructions.

It also uses gaming software called Unity 3D.

This creates an immersive world in which the jury, judges and other members of the court can explore and see in 3D high-resolution detail - similar to Star Trek's hologram setup.

'In Switzerland, scenes are routinely reconstructed by combining 3D laser scans of the scene to post-mortem surface scans and medical images, such as CT and MRI,' explained lead researcher Lars Ebert from the from the Institute of Forensic Medicine in Zurich.

 To demonstrate the system, the researchers chose to reconstruct a shooting in an internet cafe (pictured). The scene was recorded by a surveillance camera, and the team then used a laser to scan the surroundings. The aim was to show how close bullet trajectories came to injuring people in the room

HOW DOES THE FORENSIC HOLODECK SYSTEM WORK? 

The low-cost setup uses an Oculus Rift headset, the OptiTrack optical tracker, a laser scanner from Geomagic and Autodesk 3DS Max software to create the final reconstructions. 

This creates an immersive world in which the jury, judges and other members of the court can explore and see in 3D high-resolution detail.

Oculus Rift is worn on the head and measures the orientation of the wearer in real time, allowing for calculation of the scene with the correct perspective.

Oculus Rift (pictured) is worn on the head and measures the orientation of the wearer in real time

The headset consists of a screen that is split in half, delivering half the 1280 x 800 pixel resolution for each eye.

In the front of the screen, two plastic lenses help create a diagonal viewing angle of 110-degrees.

The Rift is then connected to the PC using a HDMI cable, and a USB transfers information about the head orientation to a computer.

Head orientation is measured using a combination of gyros, accelerometers, and magnetometers.

When used for gaming, the headset doesn't typically need to use positional information of the head is usually not required.

To overcome this problem for the forensic holodeck system, the researchers added an optical tracker to measure the user position.

This meant they could freely move inside the virtual scene. 

To demonstrate the system, the researchers recently chose to reconstruct a shooting in an internet cafe.

The scene was recorded by a surveillance camera, and the team then used a laser to scan the surroundings.  The aim was to show how close bullet trajectories came to injuring people in the room.

'The purpose of these reconstructions is to create a visualisation of an event to make it possible for a state attorney or judge to properly assess a situation based on the bullet trajectories, visibility, speed and distance.'

Mr Ebert continued, however, that although the data used for these reconstructions are high resolution, and allow for a spatially correct display of the scene, they typically use a 3D reconstruction on a 2D display.

This reduces the amount of spatial information available.

The technology is similar to the fictional holodeck in Star Trek (pictured with Deanna Troi played by Marina Sirtis left and Jonathan Frakes as William Riker right). Holodecks were installed on starships, space stations, and at Starfleet for entertainment, training, and investigative purposes

And although 3D screens partially solve this problem, estimating distances is still difficult because the perceived depth depends on the size of the display.

Mr Ebert believes his Oculus Rift system is a solution to this.  

To demonstrate the system, the researchers recently chose to reconstruct a shooting.

During the incident in an internet cafe, a known drug dealer was approached by policemen and women in civilian clothes as well as in uniform for the purpose of arresting him.

Despite being surrounded, the man was able to get up from his chair and draw a handgun.

One of the policemen managed to grab onto the arm bearing the gun while the others attempted to take cover.

In the course of the struggle, seven gunshots were fired and one of the bullets hit a policeman on his hand.

The entire scene was recorded by a surveillance camera in one of the top corners of the room, and these recordings were used to reconstruct the sequence of events.

The team then used a laser to scan the surroundings, and used to this to pinpoint the final position of the projectiles. 

This, along with the camera footage, were used to reconstruct every bullet fired.

The aim of the reconstruction was to show how close the bullet trajectories came to severely injuring one of the people in the room.

'During a police congress, we were able to demonstrate the system,' continued the researchers. 

'The comments by the police officers involved in the presented incident were promising.'

Further work will be carried out to make the technology more accurate before it is used widely in courtrooms.  

'The forensic holodeck: an immersive display for forensic crime scene reconstructions' was published in the Springer journal Forensic Science, Medicine, and Pathology.