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Related to this: Death note handwriting check

A lot of DNA must have rubbed off on the Death Notes. Unless the Death Note has a rule about fingerprints or DNA, I don't see how this isn't a plothole.

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BCLC
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    i think its going to be hard to answer this without a lot of knowledge on forensics. With that said, thumbprints are a result of oil, without some surface that is conducive to lifting the oil as it was imprinted, it wont happen. Paper absorbs the oil so you can't really get prints off of them AFAICT, There has to be a certain amount of DNA to sequence. I'm not sure if there is enough – ton.yeung Oct 14 '15 at 22:40
  • @ton.yeung What? I think that in general books can examined for DNA. I'm guessing the Death Note has a rule for such things. If not, this seems to be a plothole. – BCLC Oct 14 '15 at 22:41
  • @ton.yeung Oh drat. I guess forensic knowledge is needed. You mean to say just because you press your finger on a book doesn't mean that your fingerprint will be there? I see in a lot of movies and series that people shine some fancy flashlights on walls or guns and then can see fingerprints. So that's just artistic license? – BCLC Oct 14 '15 at 22:45
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    i am quite sure the entire task force touched the Death Note to see Rem. unless they did the testing before then there would be (to my knowledge) no way to check if Light had touched it previously as his fingerprints and DNA could just have been from when the task force touched it – Memor-X Oct 14 '15 at 22:46
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    @BCLC memor makes a good point, i didn't watch the series so i didn't know about that. the notebook would definitely qualify as contaminated by that point. I think that means its *nearly* worthless from a forensics standpoint. And yes, lots and lots of artistic license, and then a healthy helping of bs. – ton.yeung Oct 14 '15 at 22:48

2 Answers2

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When the Kira Task Force recovered the Death Note from Kyosuke Higuchi there is 2 things which contaminated any DNA evidence on the Death Note:

  1. The Kira Task Force touched the Death Note to see Rem
  2. Light was holding onto the Death Note as part of his plan to reclaim ownership (when his memories returned)

To my knowledge there is no way to tell "when" fingerprints or DNA first made contact with an object being tested as such any of Light's DNA found on the Death Note can easily be explained by his interactions with it when the Death Note was recovered.

Remember that the idea was to capture Kira and convict him in a court of law and DNA on the Death Note would be inadmissible due to how it was handled. This is why the police tend to block of crime scenes ensure that the proper Chain of Evidence is met. In some cop shows there are times that, when a seal is broken or multiple undocumented people handled a particular piece of evidence, it can't be used in court.

Even if Light didn't touch the Death Note when it was recovered and L found Light's DNA on it, suspecting Light again after the 13-day rule seemed to show his innocence would not help L since up until now Light had been very cooperative in aiding the Task Force and they were all on good terms. He would first need to prove to the rest of the Task Force/Police that the 13-day rule is fake thus returning to what I have explained here and then rule out any other way Light's DNA could have gotten onto the Death Note after it's recovery.

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Memor-X
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  • That about sums it up probably. Though I honestly don't think they would've found much by way of DNA even without being contaminated. Light knows about that and is anal about it. The switching of notes happens with him using a handkerchief to keep his DNA off it and I wouldn't doubt he wiped them both clean beforehand to clear him and Misa on the chance that they did try forensics testing. – Lenora Mar 07 '16 at 19:00
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Since my answer at the linked question answers this question as well, I will only copy it in a quote:

After handing over the Death Note to Rem in the plan to free Misa out Light says (chapter 54):

enter image description here

In other words, he tore the pages out and checked there's none of the fingerprints or his handwriting, so it's no surprise that L didn't check out the handwriting since there weren't any other names written beside Higuchi's.

All though it didn't mentioned in the anime, it's unthinkable that Light would missing do such an obvious thing.

And as for hair and DNA as mentioned in the question, I think it's obviously.

BCLC
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  • I find it weird that Light could somehow completely wipe out all traces of physical evidence, but eh at least it was mentioned. Thanks! – BCLC Oct 12 '20 at 08:25
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    it's light we are talking about, the one who even were ready to burn all his desk and family so the Death Note won't be discovered, so he won't be able to remove all his traces from the Death Note? – USerNAme Oct 12 '20 at 09:44
  • USerNAme, eh, idk. it's so hard for people like dexter, but apparently it's a piece of cake (or potato chip) for light. i just view it as part of suspension of disbelief or whatchamacallit – BCLC Feb 08 '21 at 04:42
  • @BCLC we have official source, why to think too hard on this? – USerNAme Feb 15 '21 at 12:47
  • USerNAme, i don't really buy it, but i'm not really thinking hard as to whether i should really buy it or not – BCLC Dec 11 '21 at 19:34
  • @BCLC you compared light to dexter. you should remember that dexter killed by hand with blood and all. light just had to clean the notebook from hair and stuff. lol – USerNAme Dec 11 '21 at 19:47
  • 'just' ? hair and fingerprints are really big deals i believe. – BCLC Jan 23 '22 at 09:05