It's around noon on the day before Christmas, and I'm out walking in the Syrian city of Kobane, with the local Kurdish journalist Mustafa Ali as my guide. The streets are lined with piles of broken concrete, smashed glass, and a few bullet-riddled car wrecks. Explosions rip the air, and the different sounds tell me whether they're coming from the Islamic State (IS), the peshmerga reinforcements from Iraqi Kurdistan, or the Obama administration. For half a week I've been trying to locate a very specific female fighter to interview, and we just received word that she's alive and based at the southern front.

Heading in that direction, Mustafa and I soon reach the western part of the neighborhood of Botan, and a small base of the People's Protection Units (YPG). A dozen or so young fighters wearing Kurdish fatigues are there, and they're all in a very good mood, offering smiles and cigarettes. Dayan, the 32-year-old local commander, invites us in for tea. Inside, he explains how this area was liberated from IS about 15 or 20 days earlier, partly with the help of coordinated US aerial bombardment. Two US-made M16 rifles that were said to be found with the fundamentalists are leaned up against a wall behind him.

The last few days have brought some similar advancements by the local Kurdish forces. Streets and strategic buildings have been taken over by slow street fighting, which culminated in the important December 22 recapturing of Kobane's Cultural Center. A few hours earlier, the happy fighters of this YPG unit had managed to make their own successful early morning attack against a house on the southern front, where an IS leader named Emir Abu Zahra was known to reside. They told me that in the firefight he was shot and killed.

"They also found a few things of his, which they took with them," Dayan told me.

A slightly older fighter who speaks German came back into the room where we drank tea and perused the findings. Among them was a very thick, professional Dell laptop — one of those rugged, military-style Latitude XFRs, which has a ballistic armor protection system and is sold in stores for a few thousand dollars. They are meant to be used in demanding environments by oil workers, the police, and the army. It's an expensive piece of equipment, but something you can probably easily pick up after having robbed the central bank of Mosul.

There's also a traditional looking Middle Eastern dagger among the possessions they said they took from the now dead IS leader. Surprisingly, it's not an authentic one, but a tacky copy with an Egyptian sphinx emblazoned on the case, and a horned goat head on the shaft. There are no blood traces on the blade.

And finally, sitting in front of me, is a large, transparent plastic bag filled with white powder. The YPG fighters told me they are not sure what this could be. So I dipped my index finger into it, and sure enough, it's a big bag of cocaine. I must admit, I am familiar with the taste of the drug.

"Cocaine? What is that?" they ask.

The other guys have no knowledge of this drug, or how people use it. It's nothing they have heard of or encountered before. But Dayan suggests that the powder is something Abu Zahra was distributing in smaller portions to his fighters.

There have been persistent rumors and accusations of drug use in the ranks of Islamic State fighters. Leaders in the group have been said to drug their militants to give them greater courage as they go into battle. This has led to both successful, but also reckless and ineffective suicide attacks by fighters who can easily be shot down. Certain IS militants have been described as "drug-crazed," and Kurds report having found mysterious pills, capsules, and syringes on living and dead IS fighters. And the slurred speech of the murderer behind the infamous beheadings of kidnapped Westerners, the man dubbed "Jihadi John," has been explained as him being high on khat.

All of this stands in sharp contrast to the official image that the Islamic State has been trying to present, as strict adherers to sharia law. Propaganda videos have shown IS members setting fire to piles of cannabis plants apparently found in the vicinity of Aleppo, while others have shown them breaking bottles of liquor, and even burning cigarettes and pharmaceutical drugs. All of these things are illegal under sharia law, and the group's policy on addictive drugs has officially been so strict that even smoking tobacco has been punished with chopped off fingers.

With the finding of what seems to be Abu Zahra's cocaine in Kobane, this could be the first confirmed and concrete evidence of drug use among IS fighters — and of a double standard of men who preach fundamentalism, yet are getting high as they commit massacres.