Do police officers tamper with evidence or falsify claims/accusations on rare occasions, in order to frame/scare suspects?

I have, in 33 years of law enforcement, never encountered planted evidence. The consequences of a peace officer being caught carrying an illegal substance around with him are too great - fired is the least of your worries. Beat cops frequently try to scare information out of an an arrestee/contact. This tactic sometimes works and is more likely to work with someone young, inexperienced, and with limited prior contacts with the police. The substance he was carrying would most likely be subjected to a presumptive field test for cocaine, either on scene or at the evidence locker (that's how we did it at the Sheriff's Office.) Unless melatonin is one of the substances (there are some) that shows a false positive for cocaine, that would be the end of that. I would echo Jennifer Ellis's caution about carrying a substance that could be mistaken for cocaine, especially if it's in a baggie or bindle. (Does anyone even fold bindles anymore?) The melatonin I use comes in capsules. I'd recommend carrying the capsules in the bottle to avoid this sort of thing.

As Tim Dees has noted, some law enforcement officers do "flake" suspects. When I was on loan to the DEA office in Boston in 1986 as an analyst, we put away two Boston police officers and four Suffolk County Sheriff's Deputies for arresting suspected street corner drug dealers, finding no drugs on them and then planting drugs, taken in other cases, on them to justify an arrest. They tried to justify their actions on the grounds that they "knew" the person they arrested was a drug dealer and framing a drug dealer got a drug dealer off of the street.

A2A: I agree with Mr. Carvalho. Intimidation is a common aspect of arrest scenarios. While planting evidence does happen very infrequently (a potential aspect of the “Dirty Hands Dilemma”), unless your friend was acting like a total a-hole, it is silly to assume it would happen in this kind of case. Moreover, the possibility of a cop carrying cocaine, which  is likely to jeopardize his career and risk him being sent to prison, is highly unlikely.

Your friend's lawyer is most likely correct.  It is unlikely the police switched the substance. But your friend might want to rethink carrying a substance that looks like cocaine on him.If you require legal assistance, please contact a lawyer in yo...

To add an answer with an alternate perspective: If this is a genuine question, consider applying Ockham's razor and ponder the possibility that your friend who stays up all night and snorts a powdered substance he keeps in his wallet and is now worried it will mysteriously turn out to be cocaine, is in fact a user of cocaine. Just a thought.

How often do police lie and plant evidence?  It's very hard to know.  The code of silence among police officers makes it hard to tell.  The Walter Scott shooting and video is a very troubling piece of evidence in this regard. The officer who shot Scott, Michael Slager, reported that Scott had threatened him and tried to grab his taser, and that police tried to give medical attention to Scott.  The video demonstrated that these were lies: in reality, Scott was running away from Slager; Slager shot him repeatedly in the back; Slager walked over to Scott's dying body and planted the taser to corroborate the false story; Slager's colleague was already present when Slager planted the taser; and Slager and his colleagues did not provide medical attention. The nonchalance with which Slager and his colleagues killed an innocent man, planted evidence, and filed false paperwork suggests that this was not an isolated incident for this police force.  And if not for this police force, what about other police forces?  The Justice Department review of Ferguson's police department suggests comparable levels of abuse and mendacity.     As for the frequency of putting pressure on defendants, look at the most extreme form of this: false confessions.  If a prosecutor says to you "I can put you in jail for 30 years, but if you confess I can get you 5 years," you have a reason to confess even if you didn't do it.  If you believe the system can falsely convict people (which many criminal defendants believe), then you will probably give a false confession.  Hundreds of false confessions have been later proven false by clear evidence such as DNA evidence; see this report here: http://web.williams.edu/Psychology/Faculty/Kassin/files/White%20Paper%20online%20(09).pdf (referring to the Central Park jogger case and many others). None of this is quantitative, but it does suggest that abuses are real and perhaps frequent.

Your friend can argue that due to his insomnia he'd never use cocain because coke makes one lose sleep and, hence would make his condition worst. Plus, he can submit himself to an hair test and prove that he doesn't use that drug. Obviously, the police can frame anyone. If you're smart, innocent and have a good lawyer, chances are you can prove your innocense.

There is always the possibility that your friend could be lying to you, however, assuming the facts and circumstances you present are correct; it appears your friend’s only charge is “Public Intoxication” or “Drunk in Public.” This charge is very similar to a parking ticket and is usually not part of a criminal record. The reason police arrest a public drunk is to protect them (the arrestee) and others. The only reason the drunk goes to jail is if an alcohol treatment center is unavailable (which it almost always is unavailable).The other matter is probably pending a laboratory examination to prove or disprove whether it is a controlled substance and what Schedule and type it is. Cocaine is listed in Schedule II. It is highly unlikely the police would plant or alter evidence of a crime regarding your friend. What would be the reason to do that? Most law enforcement officers are honest and try to do a good job fairly and impartially within the law. Ethically, most officers would report a rogue officer’s unethical actions. With over a million law enforcement officers of all types in the United States, a fractional percentage (less than one percent) actually commits illegal acts. Unfortunately, those are the ones people hear about.

I do not believe that most police officers would plant false evidence.  However, I have known police officers to lie in sworn depositions and on the witness stand.