First some relevant background into Swedish legal history. When the prosecution against Julian Assange was prematurely terminated, it was later restarted again by the Prosecution Development Centre (i.e ”åklagarmyndighetens utvecklingscentrum” in the original swedish) 
This department possesses that particular authority and responsibility. By which I mean the ability to start prosecution when the ordinary channels for justice cease to function. A power it rarely uses. When it is used, it is to make sure that laws are not interpreted too narrowly – thereby ensuring that illegal activity is properly prosecuted. The issue at hand, is not directly related to the Assenge-case, that case is simply brought up to illustrate the mechanism involved.
Swedish law prohibits preparations to commit crimes, as well as accepting an employment to perform illegal acts. Or giving/receiving of other payments to commit a crimes. The law also prohibits facilitating crimes. All of this is spelled out in our penalcode (i.e ”Brottsbalken”) chapter 23, paragraph 2. The law in the original swedish is linked, with other sources, in the videodescription. 
Joining ISIS is to take upon oneself an employment for the purpose of commiting crimes. This act also entails volunteering to receive payment for these criminal tasks. Traveling to ISIS-controlled territory to join the group, is also a textbook example of making preparations for crimes. According to CNN, ISIS-members had to fill out quote. ”a kind of job application for the terror group”.End quote. with the two employment options of being a ”fighter” or ”suicide attacker. Clearly the idea that their are ISIS-members who did not agree to assist the organisations terror, is a myth. At the very least, this journey to, and employment by ISIS, is definitely a case of substantially facilitating others in their criminal activity, which as previously mentioned is outlawed as well. If a man joins ISIS, only to repair cars, these vehicles are still used to transport slaves and travel to hotspots to commit murder.
Despite this, returning ISIS-members are only prosecuted for concrete violations (other than the act of preparing crimes) that they as individuals have committed. This results in the majority of them getting off Scott free. The fact that they are not all prosecuted for the preparations of committing crimes, on the basis of having joined ISIS – is a case of gross negligence. Particularly they should all be prosecuted for preparations to murder and to enslave – seeing as these too are ISIS main activities. All who joined ISIS must have known that they volunteered to commit, or assisted others in committing murder and enslavement. They have also received a salary for their willingness to perform these tasks if commanded to. Whether one can be proven to have committed one of these crimes, the standard applied currently, should not be relevant to the criminal activity of preparing to commit a crime, a preparation that is fulfilled by simply traveling to ISIS-controlled territory and joining their ranks.
But today the law is not respected. The absurd standard used today means that if two brothers joined ISIS, an arbitrary distinction could be drawn between them. Despite the comonality of them both having taken upon themselves the duty of committing murder if ordered to, both having had accepted a salary for this willingness to commit murder. But only if one brother videotaped himself committing a murder, would he be charged upon returning to Sweden. While the second brother, who did not document what he did or did not do, would walk away Scott free. As if the acts of joining a terrorist group and accepting a paycheck to follow it’s orders, where somehow benign.
As a comparison, in 2016 a man was convicted of planning a murder when he traveled to his ex-partner with a knife and an axe in his car. The women was warned by friends of the man, that he harbored murderous intentions.  Another person has been convicted of planning to steal a jacket, by cutting of the alarm attached to it.
To my knowledge, there seems to be no way of defending the current position of not prosecuting all returning ISIS-members. If prosecutions were to start tomorrow, all would not be found guilty of course, some would successfully claime to have traveled to the area for other reasons. But the people who gloated about their membership in ISIS on socialmedia, or who lack the skill to lie their way out, would at least face justice.
I have emailed the Prosecution Development Centre. Asking them to start a prosecution, and to answer why this hasn’t been done so far. They told me that the question was too unspecific to answer. They also refereed me to the local Public Prosecution Areas (i.e ”åklagarområde” in the original Swedish) subsections (i.e ”Åklagarkammare” in the original Swedish). As being responsible for the decision not to prosecute.
I have emailed almost all of these Public Prosecution Areas subsections, they have responded that no actions will be taken on the issue. I have sent an emailed to registered a police report with the Swedish security police (known as Säpo), in an attempt to start a prosecution myself.
To quote a video from Human Rights Watch: ”The [Iraqi] courts are using these [antiterrorist] laws to punish people solely for their affiliation with ISIS. They don’t require prosecutors to provide evidence of the more serious crimes ISIS fighters committed. So a person who cooked for a group of ISIS fighters or a doctor who worked at his local hospital after ISIS took over are facing the same penalties as fighters who tortured, raped and killed.”  Now I obviously don’t want civilians who happened to live and work in territories that were conquered to be charged, but the people who traveled to join voluntarily should be brought to justice. So Sweden must reach a compromise with Iraq. Continuing to let ISIS-members flee from Iraqi justice and go unpunished in Sweden is unacceptable. And let us not forget Syrian law. The current situation is an insult to all who has suffered at the hands IS.
If you are interested in my emailconversations with the Swedish authorities, I will link printscreens of them in the video description. I am spreading this information, in the hopes, that you the viewer, will help bring media attention to this issue – and that Swedish authorities will thereby feel pressured to do their job, and show some basic level of decency towards the victims of ISIS. I have mailed a ton of media outlets
, but so far I have been met by complete radiosilence. If you have any tips on how to help, I have started two forum threads. One in swedish, and one in English. You can find them in the videodescription. 
Thank you for your time.
Thornberg, Anders (2017/01/09) ”Säpo-chefen: Över 150 jihadister har återvänt till Sverige” Aftonbladet.
Vidlund, Susanna (2011/03/10) ”Kvinnorna tänkte inte anmäla Assange” Aftonbladet.
Gruber, Silvia Anna (2016/04/19) ”Fängelse för förberedelse till mord” SVT