Denver police have a new tool that could help solve crimes, but civil rights watchdogs are worried it could also violate your privacy.

In May, DPD purchased $30,000 worth of social media software that allows them to track all posts, like tweets, coming from a certain location.

They claim it has helped in shooting investigations and even the Boston Marathon Bombing.

It is legal, but on Thursday the ACLU raised questions about how the police department plans to use it.

The question stems back to 2003 when the ACLU sued DPD for creating 'spy files' on people taking part in peaceful protests.

Officers would track people in attendance and label some criminal extremists with a file that included their personal information.

In the eyes of the ACLU, the most egregious case came in the form of a 73-year-old nun named Antonia Antony who was labeled a criminal extremist involved in trying to overthrow the Mexican government, all for participating in a protest.

“There's a considerable amount of misinformation in these files,” claims ACLU lawyer Mark Silverstein. “People are going to be more hesitant to express their First Amendment rights [if they know they’re being tracked].”

Silverstein was the one who filed a class-action suit in 2003. He's curious if he'll need the same with Denver's newest investigative software.

“Do they have a policy that restricts the use of this software?” he asked. “We need to know what's going on.”

The purchase for the software was submitted for approval in March and began use in May. The gray area comes on what grounds can the police begin to target certain people.

“The focus right now appears to be to require reasonable suspicion in order to use surveillance of a social media sites of political organizations,” NEWS legal expert Scott Robinson said.

In other words, is it appropriate to identify certain people as threats simply by searching a political movement's hashtag, like Black Lives Matter?

The 2003 ruling would suggest no.

“I would hope that there would be a detailed policy spelling out what limits will be placed on Denver police officers,” Silverstein said.

Silverstein and 9NEWS are both awaiting the release of that policy from police.

On Thursday, DPD released a statement to 9NEWS saying, “The Denver Police Department utilizes the cloud based platform to identify open source posts that may assist with the prevention of violent acts and to assist with identifying criminal activity. The platform also allows the department the ability to gain an awareness on events which could have an impact on Public Safety.”

The ACLU is not claiming police are misusing the software, but rather questioning whether they're staying true to their word that they won't label people as threats without probable cause.