Russian President Vladimir Putin offered his first remarks on Wednesday’s plane crash that killed the founder of the Wagner Group private military company, Yevgeny Prigozhin, and other top officials.

In a televised address Thursday, Putin expressed condolences to the families of the 10 crash victims, who died when their plane went down near Kuzhenkino, Russia. Among the dead was Prigozhin’s deputy, Dmitry Utkin.

Putin praised the Wagner Group for making “a significant contribution to our common cause of fighting the neo-Nazi regime in Ukraine.” The company has deployed mercenary forces to frontline positions in the nearly year-long war.

The Russian leader said he had known Prigozhin since the 1990s, calling him a man with a “complex destiny” who had made “serious mistakes” but achieved results for himself and Russia, especially in recent months. Sympathizing with his family, Putin said, “ I want to express my sincerest condolences to the families of all the victims,”

Putin said the Investigative Committee informed him it had launched a preliminary probe into the crash’s circumstances. He also vowed the investigation would be comprehensive and its results disclosed publicly when completed.

Forensic and genetic testing is underway on the victims’ remains, which were transported Thursday to a morgue in the Tver region. 

The incident is a major blow to the Wagner Group, which has taken on an increasingly influential role in Ukraine and other Russian military operations abroad. It remains unclear who will succeed Prigozhin as the organization’s leader.