The press officer of the separatists called a French photographer minutes after separatists shot down what at that time was believed to be an Ukraine aircraft.
From the excellent research done by Arnold Greidanus as published in this post I copied the part of the French photographer. It shows the separatists shot down MH17.
It seems that the separatists thought they had made a big splash this time, and therefore called in photographer/commander Vtulkin from Torez, but also notified some journalists, like the LifeNews crew.
This is confirmed by a testimony from Jerome Sessini, the French award winning photographer who arrived at the crash site as the first international photographer. Just like the LifeNews crew Sessini arrived around 19:00, according to a quote in a news story published on July 18th. When awarded for his photo series on the MH17 crash a video testimony was made (referred to here) in which Sessini recalls the events of that afternoon:
“When we got the phone call from a press officer of the separatists, he said first: “We shot down a military plane, from Ukraine and for me it was like he was giving us an information to cover this. And when we were underway, and after 15 minutes, I got a call from friends, from a journalist, I don’t remember, and he said: ‘They shot down a civilian plane in Ukraine. Where are you?’ And I asked: ‘Are your sure it’s civilian?’ And he said: ‘Yeah, yeah, we have the confirmation.’ He said: ‘Malaysian Airlines plane with two hundred people on board.’”