Inside a packed, heavily guarded room in the House of Commons, reporters gathered for an update on Tuesday about the suspects involved in the poisoning of a former Russian spy in Britain this year.

If the subject matter was unusual, so were the people doing the briefing.

They were not prosecutors or counterintelligence officers or even spokesmen from Downing Street. Rather, they were researchers from Bellingcat, an investigative group founded by Eliot Higgins, 39, a blogger who began by posting on a laptop from his apartment while looking after his infant daughter.

Over the past month, Bellingcat has published a series of reports unmasking the Russian men who the British say traveled to Salisbury in March, poisoning a former spy, Sergei V. Skripal, and his daughter, Yulia.

The experience has been jarring for British officials — who, in some cases, seem to have learned of disclosures not long before the general public — and for Russian officials, who have expressed suspicion that Bellingcat is a front for Western spy agencies.