Bertino 18-1: Bullet Trajectory

Last updated 8 months ago

10 questions

Objectives and Background Information

Objectives
By the end of this activity, you will be able to:
Determine a bullet trajectory, given two reference points.
Calculate the angle of elevation, given two reference points.
Estimate the location of a shooter using the law of tangents after analyzing sketches and measurements from a crime scene.

Scenario
Someone shouts, “Shots fired!” But who fired? And from where? To answer these questions, the investigators begin by identifying the trajectory or path of the bullet.
To track the bullet’s trajectory, a line is drawn connecting two points along the bullet’s known path. These two points could be an entry wound (A) and exit wound (B) on a victim (Figure 1) or a bullet hole in a car window and an entry wound on someone inside the car (Figure 2).
The angle of elevation is the angle created by the bullet’s trajectory and the horizon. To determine the angle of elevation, draw a horizontal line (parallel to the horizon) that intersects the trajectory, and measure the angle formed by these two lines.

Using Trajectory to Identify the Location of a Shooter

A witness saw a victim fall while riding his bike. The cyclist had been struck in the head by a bullet. When the CSIs arrived, they estimated the angle of elevation of the bullet trajectory path to be approximately 24 degrees based on the hole in his helmet and on the entry wound on his head. The distance from his head to the building where the bullet was fired was 152 ft. The height from the ground to the entry wound on the victim while on his bike measured 6 ft above the ground.
Based on this information, what is the distance from ground level to the window where the bullet was fired? Use the law of tangents to calculate your answer.

_______ feet (round your answer to the nearest whole number)

Suppose this same city has an epidemic of bicyclist shooters. Given the following scenario calculate the angle of elevation from the cyclist's head and the shooter's position.

_______° (round to the nearest whole number)

A man is shot from a hotel window while sitting on the hood of his car. Use the following information to determine from which window the shot came. The trajectory angle is 25 degrees.

At what distance above the ground was the shot fired? Show your work. This will help locate the correct floor.
_______ feet (round your answer to the nearest whole number)

A bullet fired from a hotel window struck a victim. The bullet created both an entrance and an exit wound. In the "show your work" section illustrate how you can estimate from which window the bullet was fired.

The bullet was fired from the __________ floor in the hotel.

Practice Questions

Angle of entry (trajectory) = 15° and the distance to the building is 700 feet. Height of shooter ~_______  feet (above the horizon since the person could be sitting or standing and not be at ground level)

Angle of entry (trajectory) = 27° and the distance to the building is 60 feet. Height of shooter ~_______ feet above the horizon.

Angle of entry (trajectory) = 35° and the distance to the building is 85 feet  Height of shooter ~_______ feet above the horizon.

Final Analysis

Compare determining trajectories from two fixed objects such as a hole in a wall and a hole in a window with determining the trajectory of a bullet from entrance and exit wounds. Why would the evidence of bullet trajectory be less reliable based on entrance and exit wounds sustained by a victim as opposed to the entrance and exit holes in walls or windows?

Describe the significance of determining the trajectory of a projectile when trying to solve a crime. What information about a crime can be gained once the bullet trajectory path is established?

During autopsies, bullets need to be recovered and submitted to the police as evidence. Investigators have been known to drag rivers to recover a firearm. Describe the type of evidence that could be recovered from firearms, bullets, and cartridge casings that could help link evidence to a particular firearm or person.