Apparently these three journalists all died within a couple days of each other (Feb. 11 to 12, 2015). The implication of some rumours going around is that these folks were killed because they have evidence showing that the CIA had some involvement in 9/11.
There are several web-sites discussing this, with excerpts such as:
The [three plus Brian Williams] presented documents required for access to confidential documents file Kremlin (Russian Government headquarters) containing evidence linked to the attacks occurred on September 11, 2001.
The work of the four journalists sought to discover the truth of the attack on the twin towers. David Carr was who devised to make the film after seeing the audiovisual documentary Citizenfour and study each confession exanalista CIA Edward Snowden.
Were these three collaborating on an investigation into the CIA in relation to 9/11? If so, is there any reason to believe they had any persuasive evidence?