Carrie Medina got off a TriMet bus in downtown Portland when she saw two police officers arresting a young man "rather roughly.''

The self-described citizen journalist began to videotape the Feb. 12, 2013 encounter on her Droid phone and broadcast the images live on Ustream.

After nearly four minutes, Gresham police Officer Taylor Letsis approached her and demanded to see her video. If she didn't let him, he threatened to seize her phone.

Letsis, assigned to the transit police, ultimately took hold of her arm and grabbed the phone away, saying he didn't need a subpoena to search it for evidence of a crime, according to Medina's account.

Now the woman and attorneys from the ACLU of Oregon are suing the officer, the cities of Portland, Gresham and TriMet in federal court in Portland, alleging violations of her constitutional right to film police in public. The suit was filed late Tuesday, and the ACLU plans to hold a news conference Wednesday afternoon.

Included as an exhibit in the suit is a March 5, 2013, email from Gresham's police chief to his sworn officers, reminding them that he highly discourages the seizing of property "for simply recording your official actions without your knowledge.'' The email was issued less than three weeks after the officer's confrontation with Medina.

According to the lawsuit, Medina had offered to provide the video footage to the officer if he gave her a subpoena. After he grabbed the phone, a prompt popped up on the Ustream app to archive the video. Medina, concerned the officer wasn't going to save the video, urged him to archive it. He did, and she then walked him through the process of posting it to a social media site, the suit says.

The officer handed the phone back to Medina and ordered her to show him the video and she complied, since he had posted it for her on social media.

"As soon as Ms. Medina pressed 'play' to start the video, Officer Letsis grabbed the phone from her a second time,'' the suit says. "Officer Letsis did so without warning, and without the consent of Ms. Medina, despite the absence of any probable cause - or any reason at all - to suspect either that Ms. Medina had committed a crime, that the phone contained evidence of a crime, or that the evidence (which he himself had just archived to the Ustream web server) was in any danger of being destroyed.''

When Medina, who goes by the Twitter handle CarrieFoTruth, presented the video to the news media days later, a Gresham police spokesman said Letsis' conduct was legal, the suit says.

But in Gresham Police Chief Craig Junginger's March email to his force, he reminded officers that they can seize cellphones if there's probable cause to believe the recording contains evidence of a crime.

But Junginger warned that if the property isn't at risk of destruction, officers must obtain a search warrant to download the video.

"I highly discourage the seizing of property or the arresting of persons, for simply recording your official actions without your knowledge,'' the email said.

The suit alleges the officer violated Medina's First Amendment right to record and broadcast audiovisual footage of public activities of police and disseminate that coverage to the public live, and her Fourth Amendment right to be free of unreasonable search and seizure.

It alleges Portland, Gresham and TriMet police who make up the Transit Police Division failed to adequately train and supervise the officers who were making the arrest about the constitutional right to film police in public. It alleges transit police officers in general had a "widespread'' practice of seizing people's cameras to search for video footage.''

Medina is seeking a court injunction that would require the defendants to impose new polices and training to "recognize, uphold and protect the right to record and broadcast live audiovisual footage of police activities in public.''

"Police should always act as they would if they knew there was a camera rolling," Medina said in a prepared statement.

"The right to record and broadcast the public activities of police is protected by the First Amendment and provides a critical check and balance on the tremendous power entrusted to police," said Jann Carson, associate director of the ACLU of Oregon. "The widespread availability of recording technology makes it imperative that police agencies clearly direct and train all officers to respect the public's right to film police activities.

The suit contends she suffered physical and psychological injuries, the interruption of her live broadcast and loss of footage that she otherwise would have captured, as well as an invasion of privacy. She's also seeking more than $2,000 in damages and attorney fees.

According to the suit, Medina is a research assistant at OHSU, where she manages an employee wellness program and promotes OHSU events on social media. She also is a co-founder of Film the Police Portland, a group dedicated to improving police accountability through the videotaping of police encounters.

She says in the suit that she serves as a "camera of accountability'' and has reported on Occupy protests, a bike accident and the pepper-spraying of a high school student.

--Maxine Bernstein

mbernstein@oregonian.com

503-221-8212; @maxoregonian