The four teenagers arrested after a robbery at a luxury watch shop in Tokyo’s Ginza district earlier this week were sent to prosecutors on Wednesday, with investigators saying the suspects have claimed they don’t know each other.

The Metropolitan Police Department will analyze smartphones used by the suspects — a 16-year-old, an 18-year-old and two 19-year-olds — and probe their relationship and how they came together before the Monday robbery.

A group of three masked assailants threatened the shop’s staff with a knife before smashing showcases and placing merchandise into black bags, eventually escaping in a rental car. There were five staff members in the store at the time but no one was injured.