LONDON — An international investigation that found four men responsible for the downing of a Malaysia Airlines jet in eastern Ukraine in 2014 has also revealed the chain of events that led to the deaths of the plane's nearly 300 passengers and crew.

Separatist rebels had asked Russia for advanced military hardware to help them in their fight against Ukrainian government forces. But a Russian-made Buk missile was used instead to bring down the civilian airliner, investigators said.

The group's findings allege high-level collaboration between the Kremlin and Russian separatist fighters in Ukraine when the jet traveling from Amsterdam to Kuala Lumpur was shot down without warning on July 17, 2014.

The Joint Investigation Team was so confident in its findings that on Wednesday they charged four men — three Russians and one Ukrainian — with the murder of the 298 people on board Flight 17.

What was the evidence that convinced them who was responsible?

At first the Dutch-led investigation’s progress was slow. Families of the dead were distressed by conspiracy theories that began to circulate before any official account of the attack could counter them.

Then in 2015, the Dutch Safety Board concluded that the plane was shot down from eastern Ukraine. And in September 2016, the investigation team said it had identified the kind of weapon used: a 9M38 missile fired from a Buk Telar, a Cold War-era rocket launcher that was brought in from Russia and was taken back after the place was downed.

But it took until May 2018 to establish which specific launcher was used: The investigation team published grainy video footage of a military convoy that it said proved the launcher came from the Russian army — specifically the 53rd Anti-Aircraft Missile Brigade. It was identifiable by the numbers 3 and 2 on its side.

At this point, the team was investigating some 100 people with some link to the launcher. Through finding witnesses, satellite imagery, wiretaps, forensic evidence and huge amounts of intercepted phone metadata, this number was whittled down to four.

One of them, Igor Girkin, 48, a former colonel in the FSB, the Russian security service, played a key role in securing the rocket launcher and its transportation and use in eastern Ukraine, investigators allege.

They said the other three men charged with murder — Sergey Dubinsky, 56, Oleg Pulatiov, 52, and the Ukrainian, Leonid Kharchenko, 47 — all answered to Girkin.

On Wednesday morning, before the indictments were announced, the investigative journalism site Bellingcat alleged that these men, along with several others, played a direct role in the attack.

Graphic provided by the Joint Investigation Team into the MH17 crash.

Girkin had been appointed minister of defense of the self-proclaimed People’s Republic of Donetsk in eastern Ukraine, which although not internationally recognized as a state still had a political and military hierarchy that had regular contact with Moscow while it fought Ukrainian forces.

It was from this region that investigators say the plane was shot down. But early in the investigation, detectives didn't know the how the launcher came to be in Russia.

In 2015 the investigation team published the transcript of an intercepted phone conversation between Dubinsky and a Russian associate at 8.06 a.m. on the morning of July 17 — the day of the attack — that indicated that both the launcher and its crew came from the Russian army's 53rd Anti-Aircraft Missile Brigade.

Another intercepted conversation featured a Russian soldier traveling with a convoy that included the same Buk launcher investigators had identified, with the numerals 3 and 2 on its side.

Chatting online with a mystery woman identified only as “Anastasia,” the soldier confirmed he was traveling with the third battalion — the unit investigators say was responsible for firing the rocket.

Anastasia asks which direction the third battalion went after the soldiers's unit, the second battalion, parted ways and he hints that they traveled west. When she suggests to Ukraine, he replies: “Look, you are not only beautiful but also smart.”

Photo released by Dutch police shows soldiers of the 53rd Anti-Aircraft Missile Brigade in the summer of 2014 close to the time when MH17 was shot down. Politie Nederland

According to investigators, evidence indicates that pro-Russian forces in Ukraine were desperate for anti-aircraft support to come to their aid in the fight against Ukrainian forces.

One piece of evidence was a wiretapped phone call (originally released by the Ukrainian Security Service) on June 8, 2014, in which Girkin pleads for help from an employee of Sergey Aksyonov, the Kremlin-appointed leader of Crimea, the Ukrainian peninsula annexed by Russia in March 2014.

“If no large-scale support arrives in the nearest time they will strangle us then we’re done,” Girkin says. “What we need is large-scale support. What we get is already not sufficient.”

He asks for anti-aircraft artillery and anti-aircraft artillery with trained personnel because, he points out, there is no time to train anyone.

Then 15 minutes later, as another wiretap shows, Aksyonov himself calls back and says he will get in touch with “those who have already made this decision.” Adding that he doesn’t want to mention names over the phone, Aksyonov reassures Girkin that the situation is being dealt with.

The Russian Ministry of Foreign Affairs said on Wednesday: “The Russian Federation once again finds itself the target of completely unfounded accusations intended to discredit it in the eyes of the international community.”

An armed pro-Russian separatist stands on part of the wreckage of MH17 three days after it was brought down in July 2014. Maxim Zmeyev / Reuters file

Some 50 detectives and 25 other full-time staff are working on the investigation, including some based in Kiev. While the alleged ringleaders have been identified, it's still unknown who pressed the button to fire the missile and investigators are appealing for witnesses.