Homicide Investigations: How to Determine Time of Death

Most people are familiar with how Hollywood handles death. A weary doctor mutters “Call it” in a TV drama after a medical team did everything they could but still couldn’t save someone from the cruel hand of fate; in other stories, the time of death is declared just before the dying character experiences something spiritually transformative which pushes him or her back into full consciousness. Regardless the outcome, heartbreaking or heartwarming, that moment demonstrates the usefulness of a supervised death in a clinical setting. Medical center staff can pinpoint the instant a patient succumbed—a point in time that may be disclosed to everyone from insurance companies to law enforcement.

It’s a different story, however, for an unattended death, especially one that may be declared suspicious and when violence clearly took place. In these cases, law enforcement must use a combination of investigative techniques and science to calculate how much time elapsed between the victim taking their last breath and their remains being found.

Knowing this figure could be useful when trying to discover the circumstances of a victim’s death, including what time-related questions to ask possible witnesses and suspects and what other evidence to focus on. For example, if surveillance photos are available, are they needed from the preceding two hours or two days?

An accurate time of death also can help rule out possible suspects who may have been somewhere else when the death occurred and a more general time range could create a larger window for someone’s alibi. This information can be used in court to establish a case.

While some officers seek clues by interviewing people associated with the victim, other crime scene investigators may utilize scientific methods of observation and examination to come up with a fairly accurate time of death. Of course, this process is difficult and requires advanced training to know where to look and how to measure variables; not surprisingly, the information needs to be precise, accurate, and able to stand up in court, especially when defense attorneys go out of their way to question every action and procedure.

Several occupations contribute to homicide investigations, including crime scene technicians, who analyze and process evidence or medicolegal investigators, who focus scientifically on how a death occured. These can be rewarding professions since they not only help law enforcement track down killers and bring closure to families, but they also make decent money in the process. The U.S. Bureau of Labor Statistics (BLS Oct. 2017) reported that the median annual wage for forensic science technicians was $27.29 per hour or $56,750 annually. Furthermore, it’s a field poised to grow much faster than average in the coming decade. In fact, the BLS anticipated a 17 percent increase in openings for these trained professionals between 2016 and 2026—an increase from 15,400 to 17,000 nationally.

The drawbacks to working in this environment are obvious; death scenes are by nature messy, and unattended deaths may be even less appealing with the prospect of gore and decomposition. Assessing time of death also may require manipulation of someone’s remains and examining their organs right at a crime scene—not just measuring blood spatters or looking for bullet trajectories.

This guide offers a summary of how investigators typically determine a person’s time of death and features several college programs to help aspiring forensics professionals learn the tools of the trade.

A Brief Overview of How to Determine Time of Death

The body always tells a story, especially when the heart stops beating. There’s a generally predictable process of shutting down, cooling off, and decaying, which can be used to approximate when death took place—whether it’s hours, days, or years. In some cases, a basic assessment of a body may be required at a scene, and other times it must be taken to a lab for more detailed forensic analysis.

Experience and training can help provide guidance on what is observed in these scenes. While traditional methods of observation still have their place, there are also newer methods that help provide a better picture of the chronology. Since there’s still scientific debate on the most accurate methods, doing a variety of measurements can present a more comprehensive picture. This includes:

• Body temperature – A living human has an average temperature of 98.6 degrees F. When circulation ceases, it begins to cool, on average of 1-2 degrees every hour, until it reaches a room’s ambient temperature. Items in a patient’s bloodstream can affect this, such as alcohol. A special thermometer in the chest cavity can provide this figure.
• Degree of rigor mortis – As a body stops working, muscles begin to stiffen and contract, sometimes within 15 minutes of death. The body is typically at a full rigor situation about 15 hours after death.
• Degree of decomposition – This isn’t necessary an indicator in more recent deaths, but older deaths may require observation and comparisons of the condition of skin, bones, and organs.
• Contents of stomach/digestive system – The state of digestion of someone’s last meal can give investigators an idea of the last time they ate, what it was, and how far it moved through the intestines.
• Eye condition – Immediately after death, pupils become relaxed and dilated and don’t react to light. But over time, they contract and any optic fluid will begin to dry. Irises may also change shape.
• Skin condition – With no blood flowing, skin becomes white and less elastic. Lips may also become dry. In drowning situations or bodies submerged in water, the skin may dissolve at a certain predictable rate.
• Blood pooling – Because blood no longer flows, it may pool inside areas of a body, especially if the body is at an unusual position. So signs of pooling may indicate recent death.
• Oral conditions – A relatively new subfield of forensic research looks at the state and quantity of bacterial microbes in the mouth to estimate time of death. Different microorganisms may become more active if a person when a person is no longer walking, talking, eating, or brushing, especially if a body is decomposing.
• State of trauma – Fresh blood from an obvious wound can indicate recent death, while the condition of dried blood shows trauma happened at a certain time in the past. But beyond this basic observation, it can get legally tricky to look at some wounds for a time reference. Bite marks, for example, used to be used as evidence connecting to a suspect. This process has been placed in doubt due to how skin changes after death and how difficult it is to establish that it’s a certain bite pattern or even human.
• Insect activity – Another developing investigational field is forensic entomology, where the types, amounts, and ages of different types of bugs around or inside a body can give an indication of how long it has been in that particular place. The presence or condition of certain insects can also help investigators determine if a body may have died in one place and was moved to another one.

(Please note that this list doesn’t discuss how to interpret exactly when the “moment of death” occurs in a clinical setting, such as when doctors try to determine if a patient is officially brain-dead or still could be resuscitated or placed on a ventilator. Thankfully, this is an ethical topic that the medical profession—not the forensic industry—is wrestling with.)