— -- Turkish police have released chilling new details in the New Year's massacre at a nightclub in Istanbul that killed 39 and injured dozens more.
The suspected shooter is believed to be from the Central Asian country of Kyrgyzstan, Turkish police sources tell ABC News.
The man, whose name is known to authorities but has not been revealed, arrived in Istanbul on Nov. 20 with his wife and kids and traveled to Konya, a city in Anatolia province, two days later.
The suspect returned to Istanbul on Dec. 27, most likely by bus, before allegedly perpetrating an attack that Turkish Interior Minister Suleyman Soylu condemned as "truly inhuman savagery."
The gunman, believed to be acting alone, fired 180 rounds of 7.62 mm bullets that are commonly used in AK-47 assault rifles. He also used flares to illuminate the inside of the nightclub, police said.
Police say they don't believe the weapon used in the attack came from inside Turkey, adding that the serial number had been defaced.
At least a dozen people have been arrested, including the suspect's wife, who police say claims not to have known about her husband's plans.
The gunman allegedly killed a policeman and a civilian outside of the club before "[raining] bullets in a very cruel and merciless way on innocent people" inside the club, according to Visip Sahin, the governor of Istanbul.
Most of the victims in the massacre were shot at close range or took bullets directly to the head, an official morgue report said.
ISIS propaganda channels published a statement Monday claiming that the attack was a response to Turkey's military operations against the Islamic State group. The statement suggests that the nightclub was targets because it is where "Christians celebrate their apostate holiday" although many of the 39 victims may have been Muslim.
Fifteen of those killed were Turkish, and the other 24 hailed from a diverse array of countries including Belgium, France, India, Israel, Jordan, Lebanon, Saudi Arabia and Tunisia, according to Turkish media.
The Reina club had attracted a diverse crowd of between 400 and 500 patrons from foreign countries as well as Turkey to ring in the new year.
Among the nearly 70 people injured was a small business owner from Greenville, Delaware, Jake Raak, who was shot in the leg, family members told ABC station WPVI-TV in Philadelphia. Raak's brother, Michael, told WPVI-TV the bullet may have struck his cellphone, which may have prevented him from being injured more seriously.
ABC News' Michael Edison Hayden contributed to this report.