By ANDREW ROSS SORKIN Dec. 24, 2018

The New York Times reviewed hundreds of documents including police reports, bank records and investigator notes from a decade of mass shootings. Many of the killers built their stockpiles of high-powered weapons with the convenience of credit. No one was watching.

Two days before Omar Mateen killed 49 people and wounded 53 more at the Pulse nightclub in Orlando, he went on Google and typed “Credit card unusual spending.”

Mr. Mateen had opened six new credit card accounts — including a Mastercard, an American Express card and three Visa cards — over the previous eight months. Twelve days before the shooting, he began a $26,532 buying spree: a Sig Sauer MCX .223-caliber rifle, a Glock 17 9-millimeter semiautomatic pistol, several large magazines, thousands of rounds of ammunition and a $7,500 ring for his wife that he bought on a jewelry store card. His average spending before that, on his only card, was $1,500 a month.

His web browsing history chronicled his anxiety: “Credit card reports all three bureaus,” “FBI,” and “Why banks stop your purchases.”

https://www.nytimes.com/interactive/2018/12/24/business/dealbook/mass-shootings-credit-cards.html?