When Islamic State fighters attacked the Afghan government’s communications ministry in Kabul earlier this year, they left behind homemade breaching charges, hand grenades, ammunition still wrapped in paper packaging, cracked cellphones, water bottles filled with gasoline, a kitchen knife and at least three rifles.

During the April 20 gun battle, at least seven people were killed, along with the five attackers. The extremists, who were members of the Islamic State in Khorasan, the terrorist organization’s offshoot in Afghanistan, were shot by Afghan security forces as they tried to enter the high-rise government building with the intention of killing the hundreds of civilian workers inside.

During a recent trip to Kabul, officers from the 222, an elite Afghan police detachment assigned to protect the capital, talked to The New York Times at the site of the attack. The police, who had fought the militants in the building, provided documents that cataloged the Islamic State fighters’ equipment. The officers also described how the incident unfolded.

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Among the crime-scene evidence was a serial number that pointed to the difficulty of containing attacks in a country that foreign powers have flooded with automatic weapons for decades. This particular terrorist subgroup, formed in 2015, was using a firearm that is known to the world as an AK or Avtomat Kalashnikova. It was likely more than 60 years old.