MOSCOW - Colleagues of renowned investigative journalist Anna Politkovskaya marked the 10th anniversary of her killing Friday by urging the Russian government to track down the mastermind, while the U.S. State Department noted that the failure to do so has undermined freedom of speech in Russia.

Politkovskaya, who won international acclaim for her investigative reporting exposing human rights violations in Chechnya, was gunned down in the elevator of her Moscow apartment building on Oct. 7, 2006.

In 2014, a court in Moscow convicted the gunman and three other Chechens involved in the killing along with a former Moscow policeman who was their accomplice. Another former police officer involved in the killing made a deal with authorities that allowed him to qualify for a reduced sentence in exchange for co-operation with investigators.

Politkovskaya's newspaper, Novaya Gazeta, on Friday strongly criticized the investigators for failing to determine who ordered the killing. It said that "official lies that the case has been solved cause fury."

Novaya Gazeta editor, Dmitry Muratov, recalled the shock of Politkovskaya's killing, saying "we all walked around with black faces, to make our memorial issue."

"Then we understood we needed to get down to work quickly and to carry out our own investigation," he said.

Muratov said the paper helped investigators find a key witness who offered information that allowed them to nab the perpetrators of the killing, but an official search for the mastermind of the killing has quietly fizzled.

"We are not the security services ... we can't listen to peoples conversations, carry out surveillance, call people in for questioning, call people to submit to polygraphs, the government has to do all that, these are government functions," Muratov told The Associated Press. "I really want the investigation to conclude within the lifetime of Anna's mother who is still alive."

"I don't want to allow myself to feel helpless, and so I need to go on working and we'll carry on and do what we have to," Muratov added.

U.S. State Department spokesman John Kirby praised Politkovskaya's "courage and persistence in shedding light on the horrors of the conflicts in Chechnya"

"We again call upon the Russian government to bring to justice those responsible for ordering, planning and executing Ms. Politkovskaya's murder," he said in a statement released Thursday. "Like many other journalists reporting on the North Caucasus over the past two decades, Ms. Politkovskaya was killed in retaliation for her efforts to uncover corruption, abuse and violations of human rights. Ongoing impunity for these unsolved murders continues to undermine freedom of speech and respect for justice and human rights in Russia."

News from © The Associated Press, 2016