Ukraine’s new authorities have arrested a dozen members of the country’s disbanded “Berkut” riot police. The men are suspected of participation in the February slayings of dozens of protesters in Kiev, gunned down while agitating for the ouster of then-President Viktor Yanukovych. The authorities say more arrests are to follow and they are turning their attention to other security units, including a crack Ukrainian anti-terrorist team first identified by the Daily Beast last weekend.

In a dramatic press conference by the prosecutor general and heads of the interior ministry and SBU state security, Ukraine’s new security chiefs say Yanukovych ordered the mass slayings and the snipers were under his “direct leadership”. They allege also they have uncovered evidence that Russia’s intelligence service the FSB assisted and advised Ukrainian counterparts in the bloody bid to suppress anti-government protests, leaving more than a hundred dead.

The new head of Ukraine’s SBU intelligence service Valentyn Nalivaichenko told reporters that his predecessor at SBI, Aleksandr Yakimenko oversaw the carnage in the Maidan on the orders of ex-president Yanukovych. The operation started to be put into effect on the evening of February 18 when 108 Alfa Team members tried to set up on a building overlooking Independence Square. Protesters had vacated the structure earlier because of an fire there. The Alfa members were armed with AK-47s and sniper rifles, including German Blaser hunting rifles. But the fire and smoke prevented the Alfa team from remaining in the building.

Russian experts, who had flown in that day to advise, also brought weapons, ammunition and explosives, said Nalivaichenko. The Alfa members involved are now in hiding in Crimea but some former commanders are still in Ukraine and are being interrogated. The Ukraine government is demanding from Moscow the identity of the Russian FSB officers who acted as advisers.

The authorities stress that the investigation into the killings is still in its early stages and is centering on the killing of at least 53 anti-government protesters in Kiev’s Independence Square, known as the Maidan, on February 20. Many of the dead were killed by long-distance sniper rounds. Those killings came the day before the Yanukovych government crumbled with some key government loyalists deserting the regime as a result of the bloodshed and the ousted president fleeing Ukraine’s capital for Russia.

In all at least 103 people were killed on the streets of Kiev in the months-long protest against Yanukovych, according to the country’s Ministry of Health, although the protesters put the number at 118. The ministry says 166 protesters remain missing and that 1,528 persons were injured in the anti-government clashes.

A spokesman for the general prosecutor said all of the arrested are being detained as suspects in “mass murder on Institutska Street,” which leads off the Maidan. It saw some of the worst violence in February and has been renamed by protesters as the Avenue of the Heavenly Hundred, in honor of those killed.

According to Ukraine’s interim Attorney General Oleh Makhnitsky those detained so far were members of a special “Black Unit” within the Berkut “trained for special operations including the killing of people.” He says, “They were overseen by the presidential administration,” adding that additional arrests are likely in the coming weeks.

The special operations unit provided cover for unarmed Berkut, acting Deputy Prosecutor General Aleksey Baganets told reporters. “Their task was, as they explained, although we don’t fully believe them, to shoot back at advancing protesters and allow the regular Berkut troops to retreat.” The commander of the Black Unit is among the arrested.

Gallery: Exclusive Photos of Kiev's Russian-Trained Killers

The decision to announce preliminary findings of the ongoing probe came 48 hours after the Daily Beast published exclusive still photographs of armed members of the SBU’s anti-terrorist Alfa unit and other crack special forces units from the interior ministry locking and loading on the morning of February 20 in the courtyard of the Kiev headquarters of the Ukrainian intelligence service three blocks from the Maidan.

The SBU is the successor intelligence agency to the Ukrainian branch of the Soviet-era KGB and has exceptional ties with the Russian intelligence service, the FSB, says Ukraine’s new Justice Minister, Pavlo Petrenko. He claims the former head of the agency was a Russian agent. The Alfa Team trains with specialists from Russia, according to former Russian military intelligence officer Boris Volodarsky.

The photographs, part of an archive of hundreds of pictures and video footage shot on February 20 by ordinary Ukrainians and supplied exclusively to the Daily Beast also show Alfa Team members and other crack units rotating in and out of the courtyard during the shootings. Many of their faces are visible while they are preparing for action or resting during the morning without their masks.

Today the Daily Beast is adding to the photographs published Saturday night by posting video footage of the SBU courtyard on February 20 as well as some video frames taken the following morning of suspected Alfa team members loading up a van in the courtyard with ammunition boxes before driving it away. The February 21 frames were taken hours before Yanukovych fled the capital. Team members are seen switching tags on VW and Mazda vans parked in the courtyard before driving them off in what Maidan activists suspect was an operation to rid the SBU of ordnance and weaponry that could be linked to the shootings.

Maidan leaders have expressed reservations about the set-up of the investigation into the slayings, which is being overseen by the new heads of the SBU, the police and the prosecutor general’s office. They have objected to agencies possibly involved in the carnage leading the investigation, fearing the results will be flawed, worrying that even if the new leaders are determined to get to the bottom of the shootings, there are Yanukovych loyalists in the agencies able to sabotage the probe or cover up evidence.

Some activists expressed satisfaction with the explosive preliminary findings on Thursday but others are still pushing for an outside international body to probe the killings and provide oversight.

Maidan organizer and singer Ruslana Lyzhychko, who was nicknamed the “face of Maidan” because of her role as a spokesperson, blames Moscow for the killings. “Make no mistake about it, this was the Kremlin’s operation,” she says, adding “we need to connect all the dots and eventually it will all come out. The Russian tanks along the border are not what we are afraid of—we are afraid of the people from the old regime who still sit in their offices and are selling out Ukraine.”

Some of the video obtained by The Daily Beast has been shared with the BBC for a report scheduled to air this evening. Most of it is of fast-paced activity in the courtyard of the SBU during the morning of February 20 before and during the shootings in the Maidan that started shortly after 9:00 a.m.

The intelligence headquarters occupies an entire city block above the Maidan and on the opposite side from the Ukraine Hotel where many of the dying and wounded were carried to receive emergency care from volunteer doctors and nurses.

In the first frames are members of the Alfa Team and interior ministry units wearing yellow armbands, black coveralls and green tactical vests, and carrying ammunition boxes. Their clothing is different from that worn by Berkut members, although many of the riot police were also sporting identifying yellow armbands.

Subsequent frames show two men, one of whom is wearing jeans, walking across the courtyard quickly. One of the men is shouldering three rifles. In the following frames there are four men dressed in tactical gear resting in or near a white van (the tags of the van were switched the next day) resting late in the morning of February 20. The men’s tactical vests are packed with ammunition.

The next frames show a more casually dressed operative in the courtyard carrying gear and a rifle. The next images are of four other operatives from special units, all clothed in tactical gear and helmets and shouldering weapons, ready to head out. They are loading a blue van, the tags of which also were changed next day.

The final video shots were taken on the morning of February 21 and are of three men dressed in black coveralls loading another blue van with tactical gear and ammunition boxes.

In order to protect the sources supplying the video footage and photographs The Daily Beast is being highly cautious in publishing the material. The sources are ordinary Ukrainians and are not members of any Ukrainian political parties nor connected with any government agencies in Ukraine or overseas. They are in fear for their lives.

Maidan activists are worried also about the investigation falling victim eventually to the relentless propaganda war being waged over the shootings. The identity of the killers is a source of bitter dispute between Ukrainian and Russian authorities and has prompted a trading of fierce allegations between Moscow and Kiev. Russian leaders and the ousted Yanukovych and his lieutenants have claimed variously that the snipers were either Ukrainian neo-Nazi and ultranationalist supporters of the Maidan revolution or foreign mercenaries paid by Maidan leaders to undertake the killings in a bid to discredit the toppled regime.

In his latest interview, Yanukovych repeated his insistence that he had no hand in the slayings, accusing Maidan radicals of being responsible and conducting the killings in an effort to wreck an agreement he had reached with opposition leaders to curtail his power and hold elections by the end of the year.

Russian propagandists jumped on a leaked phone conversation between EU foreign affairs chief Catherine Ashton and Estonian Foreign Minister Urmas Paet discussing the possibility that Maidan leaders were involved in the shootings. Paet says the source was Olga Bogomolets, a Maidan leader and doctor who treated some of the dying and wounded. But she says the Estonian diplomat misunderstood here.

“I was in the Ukraine Hotel and I was telling the media and foreign politicians by phone that I could prove that snipers were shooting and killing people,” she says. She admits she had no opportunity to see the wounded among the police but she says she never says protesters were involved in the killings. “The message was the same for everybody that snipers are killing protesters on the Maidan. So was it a misunderstanding.”

There have been a handful of still photographs from the clashes showing one or two anti-government protesters with rifles. Half-a-dozen policemen were killed on February 20 but the circumstances of their deaths remain unclear. According to Ukraine’s security chiefs today the Berkut shot 17 of the 53 protesters killed. That leaves 36 the victims of the other units, including Alfa, firing that day.

“During the next few weeks we will have answers to all questions,” says Justice Minister Pavlo Petrenko. The first question is who gave the command to shoot. “Yanukovych was the organizer of all the shootings and gave the go-ahead,” says Petrenko, who was in the Maidan that day protesting. “I saw the people being killed,” he says. “It was terrible.”