Eight men, several undressed on the upper body, are lying lifeless in a courtyard in Butja, Ukraine.

Around them are plastic bags with debris and emptied juice packets.

Two have their hands tied behind their backs, almost all of them lack shoes.

A bare back of the head shows traces of dried blood.

The image of the men is one of thousands that are now being spread from Ukrainian Butja - and which according to several experts constitute evidence of regular executions of Ukrainian civilians.

The Kremlin denies involvement

According to Ukraine, at least 300 civilians have been killed by Russian forces in the city, of which at least 50 have fallen victim to so-called extrajudicial executions.

The UN also believes that all indications are that civilians in Butja have become direct targets for Russian troops.

The accusations are denied by the Kremlin, which denies any knowledge of the war crimes.

Instead, it is claimed that the bodies were placed on the streets after Russian forces left the city - information that is pointed out as pure lies.

Complicated work

Determining exactly what happened in Butja based on photos is difficult, says Patricia Rakic ​​Arle, head of the Swedish police's war crime group.

- What makes investigations difficult right now is that there is still a war going on.

Those on site are observers and the military, but they can not conduct any investigations or technical investigations, she says.

She has worked with war crimes for over ten years and participated in investigations into the genocide in Rwanda and the Balkans.

She now leads the working group that will assist in war crime investigations about the war in Ukraine.

- In the first stage, we will interview the witnesses who come to Sweden.

In general, we also want to go to the crime scene, but that is not always possible, she says.

May be forced to dig up mass graves

Determining the identities and causes of death in Ukraine requires enormous efforts, which can take years to complete.

- For example, you may have to dig up mass graves to examine the bodies and determine how they were killed.

Then the next step is to determine who is responsible for the murders, or who gave the order.

It's a huge puzzle to be solved.

Can we be sure that there are civilian Ukrainians in the pictures?

- It is impossible to say at this stage.

We can only know if there are witnesses on site who can identify the people.

An image in itself can not determine what happened.