Original Publication Date: January 25th, 2021
Updated Date: April 08th, 2025
Note: This article was originally published on January 25th, 2021, and has been updated on April 08th, 2025, to remove an expired YouTube link and enhance readability.
How Blood Evidence Shapes Crime Scene Investigations
How blood is left at a crime scene or a possible crime scene can be the result of many different processes: blood pooling, blood dripping, blood spattering, or blood spraying are some of the phrases that you will hear when watching forensic television shows.
But whether it drips, pools, sprays, or spatters, analyzing blood at a possible crime scene is part of the forensic sciences. It is in a branch known as forensic serology, which is the study of various body fluids, including blood.
It is important to know that the velocity of blood as it exits a human body can reveal important information as to whether the body was alive or dead at the time of the bleeding. Furthermore, the amount of blood at a possible crime scene can also reveal the same thing.
In this blog post, I'll look at two cases that are similar in one regard: in both cases, the blood at a crime scene was used to support the notion that the decedent at the scene was already dead when he or she bled out. The first case I will look at is the infamous 1888 murder of Polly Nichols in England, assumingly by the unknown serial killer dubbed Jack the Ripper. The second case I will look at is one from Singapore from 1972 where a boy thought to have died on train tracks in a train accident was then reassessed as already dead before being hit by the train.
The Murder of Polly Nichols: A Jack the Ripper Case
Firstly, let's look at the murder of Polly Nichols. She was killed in the Whitechapel area of London on August 31st, 1888. Due to her association with Jack the Ripper, there has never been a shortage of inquest into her death and that has produced expert conjecture pertaining to her murder.
Whoever killed Polly Nichols used a knife for either stabbing or making incisions on her neck, her vagina, her abdomen, and at other points on her body. However, one Forensic Physician, known as Dr. Jason Payne-James, expressed his opinion that Polly Nichols did not necessarily die as a result of these apparent wounds. Instead, there is a suggestion that Polly Nichols was first subjected to "manual strangulation" before her body was mutilated.
Dr. Payne-James shared this perspective in the 2014 Channel Five documentary "Jack the Ripper: The New Evidence." Originally, this article included an embedded clip from that documentary, but the link has since expired.
Strangulation, as the cause of death, has been used to explain why there was no blood spray at the scene of Polly Nichols's murder. There was blood pooling but that has to do with dripping, not spraying or spattering.
The difference between dripping and spraying results from a difference in blood pressure in the arteries. When the heart is beating, the arteries are pressurized. When the heart is not beating (i.e., the body is dead), then the pressures moving the blood are less forceful. If a corpse is pierced or sliced, then the blood might ooze out instead of being sprayed. That oozing would lead to blood pooling, and it’s this process that Dr. Payne-James described in his analysis.
The lack of blood pressure in a corpse has been used to explain how a man named Charles Lechmere, the man who was once thought to have only discovered the body of Polly Nichols, might actually have been her killer despite the fact that he had no blood spray on his clothes on the night of Nichols' murder. If Jack the Ripper (possibly Lechmere) strangled Polly Nichols to death before mutilating her, then he could still have walked the streets of the Whitechapel area without blood on his clothes. In short, that he was clean of blood spray does not clear him of the murder.
The Singapore Train Tracks Mystery: A Forensic Twist
The second case that I will look at is both similar and different. The case of a dead boy found on the Bukit Merah train tracks in Singapore in April of 1972 was covered in a course I took from Nanyang Technological University ("Introduction to Forensic Science" by Professor Roderick Bates).
According to Roderick Bates, the course instructor, in 1972 a train ran over a human body on a set of train tracks in Singapore. At first glance, one might have thought that the death of the boy should be ruled a suicide—that is, maybe he placed himself on the tracks knowing that the train wouldn't be able to stop in time to avoid running him over.
However, when a forensics-medicine specialist known as Chao Tze Cheng examined the scene, he concluded that there was not enough blood at the scene to make one think that the body was alive at the time that the train ran it over. That lack of blood had something to do with the unpressurized arteries that you find in a corpse. To Chao Tze Cheng, who was one of Singapore's top forensic authorities, that meant that the boy was already dead when placed on the tracks and that he may have been previously murdered.
Key Takeaways for Forensic Analysis
Websleuths or amateur investigators should note that blood spatter/spray and blood pooling/dripping could be a clue as to the state of the corpse at the time of any stabbing or incision. With the former, spattering and spraying would suggest that the decedent was alive at the time of the injuries. With pooling and dripping, it would suggest that the decedent was already dead at the time of the 'injuries.'
In both of the cases examined, the relative blood pressure between a living person and a dead person was central to taking an investigation in a certain direction. In the case of Polly Nichols, it showed that a suspect, Charles Lechmere, was not cleared of suspicion simply due to the fact that he had no blood on him. Since the cause of death may have been strangulation, the slicing and stabbing of the corpse would not have resulted in the spraying of blood on the person who wielded the knife. In the case of the boy on the tracks, it refuted the notion of suicide via train and allowed investigators to look for a murderer. According to Professor Roderick Bates, the investigation did conclude with charges.
Sources
- Dr. Roderick Bates, Nanyang Technological University, Singapore; the facts surrounding the case of the boy on the tracks from 1972 were covered in "Introduction to Forensic Science" and were described in a lecture of his that I watched in January 2021; date of lecture recording is not clear
- Chao Tze Cheng: forensics examiner who worked on the case of the boy on the tracks
- 2014's Channel Five documentary "Jack the Ripper: The Missing Evidence"
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