One would assume a police officer's highest priority is keeping violent criminals like murderers and rapists off the streets, but due to the way that police departments in the United States are set up, officers are often given incentives to pursue low-level drug crimes instead of violent ones.

The War on Drugs has pushed police departments to go after easy arrests like grabbing a drug user off the streets. For example, over 663,000 people were arrested in the U.S. for simply possessing marijuana in 2011. That's 100,000 more than arrests for all violent crimes that year. In many cases, offenders were only in possession of a small amount of marijuana.

1. Federal Dollars.

Why so much attention on low-level drug offenders? One major reason is that police departments receive federal grants based on how many people are arrested, rather than a declining crime rate.

“Current measures inadvertently incentivize unwise policy choices,” reads a report from the Brennan Center for Justice. “Federal officials ask states to report the number of arrests, but not whether the crime rate dropped. They measure the amount of cocaine seized, but not whether arrestees were screened for drug addiction. They tally the number of cases prosecuted, but not whether prosecutors reduced the number of petty crime offenders sent to prison. In short, today’s ... performance measures fail to show whether the programs it funds have achieved 'success:' improving public safety without needless social costs.”

So, if a department is solving most of its murder cases, but doesn't make enough overall arrests, the department can lose some of its federal funding.

2. Stats.

This likely has an effect on individual officers. Just think: An officer who arrests 19 people for having some marijuana on them looks better, on paper, at the end of the month than someone who has made one arrest for a stabbing they investigated. An officer who arrested five drug users in a day also has more paperwork to do, and therefore they'll have to put in more overtime to fill out the paperwork and will have to appear in court for those arrests. They make more money and their record looks better.

Several major news stories have highlighted the amount of DNA rape test kits that have never been analyzed because police departments often claim they don't have enough time. How much time is spent instead on nonviolent offenders? Between 1963 and 2007, the amount of murder cases that were solved went from 91 percent to 61 percent . There is certainly more than one reason things have changed for police departments, including a significant rise in murders overall, but the elevated focus on nonviolent drug crimes often monopolizes the time of departments across the country.

3. Asset forfeiture.

There are even more financial benefits for police departments that focus on drug crimes. With the practice of civil asset forfeiture, where the police can confiscate property if it is believed to be related to criminal activity, police departments can take money or possessions like cars and real estate from someone without ever charging them with a crime. Since 2001, police departments across the country have seized over $2.6 billion in cash from people who never went to jail or had to appear in court. Police departments can use that money to purchase new patrol cars, guns, and whatever else is determined to be necessary. Sometimes, what is determined to be necessary includes tickets to a football game or trips to Las Vegas .

4. Quotas

Many police departments also have quotas for the amount of traffic tickets an officer gives out and how many arrests they make, and an officer could lose their job if they regularly fail to meet those quotas.

"I can tell my supervisors that I took three people to the hospital and I saved their lives. That the child that I helped deliver is healthy," a New York City officer told NPR in April. "I can tell them that. But that's not going to cut it."

Regardless of the reasons for not getting their numbers, the officers can be punished.

The Bottom Line.

Police departments and police officers operate based on the parameters set by the state and federal government. A department that lacks government funding will find another way to get funds, an officer who is underpaid will find ways to pump up their paycheck, and most officers will do what they have to to keep their job. Until the government stops encouraging policing for profit, those who protect us can only do it for the right price.