Criminal forensics experts spend much of their time reconstructing and investigating details in a crime scene to determine in which order events took place. The order that bullets struck a particular piece of glass, whether it be a window or mirror, can help an investigator determine who fired first in a gunfight or which bullet struck a victim first. This can inform a prosecutor's choice to either try a perpetrator for murder in the first degree or for a less drastic offense.
Reconstruct the glass panel. This is a time-consuming process and may take several days and the use of microscopes.
Mark the entrance points of each individual bullet hole with sticky notes.
Look closely at the breaks emanating from each hole. The initial hole will have unbroken radial cracks reaching out and creating a series of broken arcs, which make circles around the impact point. Mark this hole impact point 1.
Examine each of the other holes. If a radial is stopped by another curve or circle it was created after that arc or circle. Follow the radials of that circle back to its impact point. If the radial doesn't terminate then it was the next in the series. If it does terminate follow the radial of that circle to its impact point. Continue this process until you get to impact point #2.
Follow the process described in step 4 until all of the impact sites have been numbered.
Re-check the order you determined by retracing the radials of each impact point.
Fractured glass can be completely reconstructed only in a lab environment but a field investigator can quickly lay out major pieces of glass to determine radial lines and order of impact.
Even if bullets were fired from different angles or different sides of the glass panel, as long as the panel was not dislodged from its framing, radials will form and aid in the determination of firing order.
The exit point of the bullet through the glass is able to be determined by chipping of the initial hole. A bullet will begin to slow down as it passes through the glass resulting in a tearing of the glass instead of the shearing present in the entrance side.
Windshields and other shatterproof glass (laminated safety glass) make it harder to determine the order of bullet entry because of the spidering nature of the breaks.