Two teenage men have been arrested on suspicion of having shot and killed a journalist who had been observing disturbances in the city of Derry, the Police Service of Northern Ireland said Saturday.

Freelance journalist Lyra McKee, 29, died after being hit by a bullet while she was watching the rioting which took place late Thursday.

“Major Investigation Team detectives have arrested two men, aged 18 and 19 under the Terrorism Act, in connection with the murder of Lyra McKee in the Creggan area of Derry,” a police statement said. “They have been taken to Musgrave Serious Crime Suite,” the statement added.

The two men are to be questioned in Musgrave, which is located in the regional capital Belfast, police said.

Images released by investigators appeared to show that McKee was shot by a masked gunman who fired indiscriminately on a police vehicle that was near to where she had been standing.

Police, who have treated the shooting as a crime of terror from the outset, describing it as part of an "orchestrated plot," have asked the public to help locate the suspected gunman.

The journalist and writer, a native of Belfast, was shot in the head allegedly by Republican dissidents linked to the so-called New IRA, according to the police, while in Creggan, a residential area of Derry.

Police believe that the riots, during which more than 50 Molotov cocktails were thrown and two cars were burned, were in response to a security operation carried out in the area with raids on some properties in order to find and seize firearms and ammunition.

The Northern Ireland police service (PSNI) had received information from the intelligence services pointing to an alleged plot by Republican dissidents to attack them during the Easter weekend.

The images, captured by security cameras in the area and later distributed by the PSNI, recorded the last moments of the reporter's life, registered around 2200 GMT on Thursday when she was seen alongside other bystanders taking photos of the riot with her mobile phone.

McKee was standing near a large police vehicle with other journalists when she was shot.

The images also show a masked man holding a firearm who appears to shoot in the direction of the police vehicle.

McKee was a reference for the gay community of Northern Ireland for her work as an activist for the rights of that group.

She had been working as an editor of the digital portal based in California, Mediagazer, specialized in information about the media industry.

The tributes received by McKee from all political sectors and the journalistic community were added to those of her partner, Sara Canning, who remembered her as a "tireless activist."

“Lyra’s death must not be in vain,” Canning said. "Our hopes and dreams, her amazing potential was snuffed out by a single barbaric act,” she added.

Canning said McKee's death had left many in the LGBT community without an important advocate but also, “It’s left me without the love of my life, the woman I was planning to grow old with."