Attorney General Eric Holder formally announced Thursday that the Justice Department will investigate whether the Ferguson Police Department systematically violated the civil rights of residents, and said that investigation could be expanded to other Missouri police departments if warranted by evidence.

“I want to make very clear that as this investigation unfolds and as it evolves, we will follow the facts and the law wherever they may lead,” Holder told reporters. “And if at any point we find reason to expand our inquiry to include additional police forces in neighboring jurisdictions, we will not hesitate to do so.”

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Holder said Justice has already reached an agreement with the St. Louis police to conduct a review, which he called a “collaborative reform effort.” He said that step would review police practices in St. Louis for possible violations of peoples’ civil rights.

The department’s announcement came after weeks of protests and rioting after Ferguson police shot and killed an 18-year old black student. The violence that ensued, and the police’s reaction to that violence, led Holder to visit the town.

Holder said his visit, as well as the work done by Justice Department officials, indicates signs that Ferguson police may be violating the Constitution through its heavy-handed police tactics.

“We have determined that there’s cause for the Justice Department to open an investigation to determine whether Ferguson police officials have engaged in a pattern or practice of violations of the United States Constitution or federal law,” he said. He said the investigation would be run by the department’s Civil Rights division, and would examine many of the complaints officials have heard in their preliminary work.

“Our investigation will assess the police department’s use of force, including deadly force,” he said. “It will analyze the stops, the searches and arrests. And it will examine the treatment of individuals detained at Ferguson’s city jail, in addition to other potentially discriminatory policing techniques and tactics that have been brought to light.”

But while a formal investigation will be launched, Holder stressed that no final conclusions have been draw. “It will be fair, it will be thorough and it will be independent,” he said.