UPDATED March 8, 2015, 2 a.m. Eastern European Time
KIEV, Ukraine -- Russian authorities apprehended two more suspects in the murder probe into the killing of Boris Nemtsov late Saturday, bringing the total detained to four, state media reported.
Albert Barakhoev, secretary of the North Caucasus region's Ingushetia security council, told RIA Novosti the two additional suspects had been identified as the younger brother of Anzor Gubashev, one of two men detained earlier on Saturday who worked in a private security company in Moscow, and a man who was in the same car as the other suspect, Zaur Dadayev, when he was taken into custody.
Additionally, Russia's Interfax news service reported that Dadayev had served 10 years in the Chechen North battalion.
Earlier, colleagues of Nemtsov's in the opposition ranks uncovered a press release from Oct. 19, 2010 that shows a man also with the name Zaur Dadayev was awarded a medal of courage. They suggested the two were one in the same.
Путин награждал сержанта Заура Дадаева орденом мужества. Того самого Дадаева, кого сегодня взяли за убийство Немцова? pic.twitter.com/fVoFELQ9kV— Илья Яшин (@IlyaYashin) March 7, 2015
Phone taps and evidence left in the getaway car led investigators on Saturday to Dadayev and Gubashev -- both from the restive North Caucasus -- said Russia's Federal Security Service (FSB) Alexander Bortnikov, whose comments were carried by the state's Rossiya 24 television channel.
"The necessary operational and investigative procedures are continuing," the FSB head said, adding that Russian President Vladimir Putin had been informed of the suspects' detention. Putin has called Nemtsov's killing a "disgrace."
Nemtsov's lawyer Vadim Prokhorov welcomed the detainments. "This is good news," he said.
Bortnikov's statement on state television suggests the Kremlin wants to put its best face forward to the public and show it's taking the investigation seriously.
Ilya Yashin, Nemtsov's colleague from liberal opposition group Republican Party of Russia-Party of People's Freedom, urged investigators to be completely transparent about the evidence gathered that points to Dadayev and Gubashev.
"The FSB should clearly and publicly prove that the detainees are actually involved in the crime," he said.
Often times the state produces "reduced" evidence that allows for only the perpetrators and not the organizers of crimes to be apprehended, Yashin added.
"If the investigation is really interested in establishing the killer, it is obliged to check for involvement in the crime of high-ranking officials who criticized Nemtsov in recent years," he said. "Everyone -- including the President of Russia" should be investigated.
Nemtsov was killed when he was shot four times in the back shortly before midnight local time on Feb. 27 while while walking with Ukrainian girlfriend Anna Duritskaya in central Moscow. Duritskaya has said she "didn't see anything" because it all happened so fast.
Ukrainian authorities granted her extra protection on Friday after she complained about receiving death threats while staying at her family home 55 miles south of Kiev.
There are many competing theories about who killed Nemtsov and why. The Kremlin has denied allegations from opposition colleagues of Nemtsov that it played a role in his murder.
Nemtsov was an outspoken critic of Putin and a former deputy prime minister under Boris Yeltsin, Russia's first post-Soviet president. Many people thought him to be Yeltsin's successor. But Putin was tapped instead of him.
Nemtsov's 30-year-old daughter Zhanna Nemtsova told CNN she has no faith in the Russian investigation into her father's murder.
"I cannot blame [Putin] directly, [but] I would say that our authorities, including the president of Russia, have political responsibility as the head of state," she said.