The 17,000 force came under fire in the 116-page report, which was released Thursday. The report said the force unnecessarily injured hundreds of people, killed others, and routinely conducted illegal searches and seizures without warrants.
"The public's demands for remedial action are fueled in part by the appalling number of officer arrests and convictions for serious misconduct and criminal activity," the report stated.
The report found that police have used "unnecessary and unreasonable" deadly force while arresting people who posed little or no harm and who did not resist.
"Many subjects of excessive force were, at the time of the incident, carrying out ordinary activities or committing minor infractions," it said.
The police department has been criticized, by Rep. Luis Gutiérrez (D-Ill), among others, for its response to the student strike and protests at the University of Puerto Rico.
The Justice Department also said police in Puerto Rico appear to routinely discriminate against people of Dominican descent and that "there is troubling evidence" that they fail to investigate sex crimes and domestic violence, the report said.
"The unconstitutional acts that we have identified arise at a time of crisis in public safety," it added.
"Contrary to national trends, violent crime increased overall in Puerto Rico by 17 percent from 2007 to 2009," the report said. "In 2010, Puerto Rico saw the second highest number of murders in its history, a trend that is escalating in 2011."
Some Puerto Rican officials maintain that drug trafficking and social deterioration are fueling the wave of violent crime.
"However," the report said, "increasing crime cannot be used to justify continued civil rights violations or the failure to implement meaningful reforms."
The New York Times first reported on the study, which was posted Thursday on the Justice Department's website.
Based on reporting by The Associated Press.