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Can paint cover up human blood on a wall?


Can paint cover up human blood?

I saw a post today that reminded me of the McStay case.  The post, which had nothing to do with the McStay’s, joked how they would paint over the blood to hide the evidence, and I began to wonder if this was done at crime scenes.   I was thinking If some random person makes this random statement, maybe this is a common method of covering up a crime scene that I have never heard of before.

mcstay family
McStay family murdered and found in graves in the desert.

We know that the San Diego Sheriff’s Dept. (SDSD) felt no foul play had happened in the home and it was not until the San 
Bernardino County Sheriff’s Dept. took over the case and arrested Charles “Chase” Merritt as a suspect in the murder of the McStay family that it was revealed they believed the murders happened in the home

If so, then why was the blood not seen when the SDSD was there?  In fact, there is a big social media debate on whether they were actually killed in the home because it is not clear whether any blood was every found in the home.  The method of murder certainly would have left blood in the home.  

Did Police used Forensics to Look for Blood?

We are not 100 percent sure if the SDSD ever used forensics to look for blood in the home, and we really don’t know if the SBCSD later found evidence of it themselves, but if they believe the murder happened in the home, then surely there must have been something that led them to that conclusion.
“One of the attempted ways to clean a scene is to paint over the blood stains, though a correct forensic processing of the crime scene would still show the blood stain, the blood stain would not be visible to the naked eye,” San Bernardino County Sheriff’s detective Joseph Steers said. “The blood stain could still be detected by forensics experts years after it was painted over.”


Really?  So, if blood was painted over, was it done with one coat, two?  And how do they know it is under the paint?

Blood Detection Experiment

Thomas Adair did an experiment on the detection of blood under paint in 2005.  His team found that blood was visible under three coats of paint and when the area was photographed it appeared dark.  Interestingly they were able to extract DNA without having to separate the blood from the paint.

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All digital cameras have a filter that blocks out infrared light, so you just have to open that sucker up and switch out that filter with an IR filter. It’s really that simple, though I don’t recommend you tear apart your expensive 5D or anything—unless you know what you’re doing.

Second Experiment

In a separate experiment horse blood (why horse I do not know but I won’t go down that road) was put on drywall.  Using a slate blue color they took their time to paint the wall, even waiting 12 hours to a week of drying time examining and photographing the results between coats under different light sources.   Their findings was that faint blood could be seen after two coats as a very light brown color, but the third coat of paint the blood was no longer visible, although the heavier blood splatters could still be detected.  On the fourth coat of paint the blood could no longer be seen at all, not even as a darker color.  With even more experimenting Adair did find that a particular photography setting with a deep yellow filter could make bloodstains visible under four coats of paint. Interestingly, after the fourth coat of paint, luminol did not react to the blood underneath.  

2010 Experiment

In 2010, Howard and Nessan used an IR illuminator and were able to detect four coats of paint.    Farra, using IR photograph was able to reveal bloodstains under six layers of paint depending on the pigments in the paint.  White paint provided the least concealment with light photography, but prevented IR detection after only two layers.  Where black paint concealed the blood in a photo after one layer.  But, several layers of paint were needed to block IR transmission.  Bottom line, the thickness and pigments of the paint have a bearing on how much paint is needed to conceal blood.  

We now know that blood that was completely invisible to a standard digital camera under two coats of paint, could be seen in infrared even under six layers.


In all of these cases, it wasn’t so much about how many coats of paint it took to cover up blood, but how they could gather the blood evidence under the paint.  Did the SBCSD use a method that has been perfected and utilized by police since 2005 to get to the blood underneath the paint on the wall, and preserve it as evidence in the McStay case?  Is this how they are sure the McStay’s were killed in the home?

Mettias, Merritt’s attorney has stated that there has been no evidence presented to show blood matching the McStay’s was found in the home by the SBCSD.  He also said there was no physical evidence found to indicate the killings occurred there.  We will have to wait till trial to know if blood evidence was truly found or not.

You might also like to read:  Myths about Luminol and Blood Detection

To read more stories about the McStay’s or the latests on the man that was arrested for their murder, Charles Chase Merritt, please type in McStay or Merritt into the search box on the top right of the page.  


2 thoughts on “Can paint cover up human blood on a wall?

  1. Paint will “cover” blood, but,the blood is still there and painting over the blood actually seals the proteins in place. There are chemicals that react with these proteins, such as Luminol, (from the word Luminous)…The luminol “highlights” these proteins which can be seen by using a black light…even through paint.

    I think the investigators dropped the ball on this case.

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