Not to mention it's trivial to leave gunpowder residue on a corpse you know was carrying...

Would hardly be the first time, just a random sample from the last 5 years:

https://www.youtube.com/watch?v=ds6g-QyAxbw

https://apnews.com/article/gun-violence-crime-baltimore-82fa...

https://www.nbcnews.com/news/us-news/st-louis-officer-execut...

https://nypost.com/2020/01/03/nypd-cop-caught-planting-stun-...