WASHINGTON (CNN) -- Miami police have engaged in a pattern of excessive use of force through officer-involved shootings, the Justice Department said on Tuesday.

The Justice Department conducted a comprehensive investigation and found that officers intentionally shot at people on 33 separate occasions from 2008 until 2011 and the police department concluded three of those instances were unjustified. The Justice Department said a number of additional shootings were "questionable at best."

The findings also noted that seven officers participated in more than a third of the shootings in question.

The Justice Department also concluded the police department did not conduct timely investigations of such shootings. In addition, the findings said the police had "deficient tactics" and that improper actions had been taken by specialized police units.

The review started in November 2011 after seven young African-American men were fatally shot by officers over eight months.

Community leaders appealed to the federal government to take action.

Roy Austin, the deputy assistant attorney general for civil rights, said there had been a similar investigation of the Miami Police Department a decade ago. Officials thought improvements had been made and closed the case without obtaining a court-supervised agreement.

Austin said the Justice Department this time plans to get a plan that would fall under judicial oversight.

"Miami has to reform deadly force and has to do it for a sustainable period of time so we don't have to come back in a decade," said Austin.

The civil rights investigation looked only at patterns within the police department and did not address whether specific officers should face criminal charges.