They didn't need DNA from the bullet, it was taken out of his body. Unless you think that Davilas was a body double.
Or maybe the suggestion (and it's only a suggestion here, you've really said nothing about what you were TRYING to prove with this section, other than that someone didn't do good police work) is that they replaced the bullet from his body with a different bullet that would trace back to Ramos.
Except that nobody is disputing that Ramos shot at the guy (and hitting him wasn't a criteria for their criminal charges). And if they switched bullets, they did a lousy job, because the bullet was inconclusive to match with the gun (which again didn't matter because nobody disputes that Ramos shot at the fleeing suspect).
So what exactly is this supposed to "rebut"? What does not having a "good chain of evidence" for the bullet do to the case against Ramos and Compean, which is based on their own testimony that they shot at the guy.
BTW, I'm not even certain anybody was trying to keep a "chain of evidence", nor am I certain that an investigator holding the bullet "violated the chain of evidence" although to my untrained mind it could.
And in fact, the summary of your section spells out the entire problem with the pro-BP crowd: "These careless actions needlessly cast suspicion on this aspect of the prosecutions case."
Except "needlessly" is more to the point "meaninglessly".
You stated the rebuttal was easily debunked. You haven't debunked anything. Did Christopher Sanchez break the chain of custody of did he not? Did he take the smuggler to his house or did he not? Did the lab destroy the DNA on the bullet or did it not? If none of these statements are true then provide the relevenat facts. This is how you debunk something.