James Vincent, reporting for The Verge:
As reported by The Philadelphia Inquirer, at the start of their investigation, FBI agents only had access to helicopter footage from a local news station. This showed a woman wearing a bandana throwing flaming debris into the smashed window of a police sedan.
By searching for videos of the protests uploaded to Instagram and Vimeo, the agents were able to find additional footage of the incident, and spotted a peace sign tattoo on the woman’s right forearm. After finding a set of 500 pictures of the protests shared by an amateur photographer, they were able to clearly see what the woman was wearing, including a T-shirt with the slogan: “Keep the Immigrants. Deport the Racists.”
The only place to buy this exact T-shirt was an Etsy store, where a user calling themselves “alleycatlore” had left a five-star review for the seller just few days before the protest. Using Google to search for this username, agents then found a matching profile at the online fashion marketplace Poshmark which listed the user’s name as “Lore-elisabeth.”
A search for “Lore-elisabeth” led to a LinkedIn profile for one Lore Elisabeth Blumenthal, employed as a massage therapist at a Philadelphia massage studio. Videos hosted by the studio showed an individual with the same distinctive peace tattoo on their arm. A phone number listed for Blumenthal led to an address. As reported by NBC Philadelphia, a subpoena served to the Etsy seller showed a “Keep the Immigrants. Deport the Racists.” T-shirt had recently been delivered to that same address.FBI used Instagram, an Etsy review, and LinkedIn to identify a protestor accused of arson