Aircraft’s last known position and speed show it climbing with decreasing speed. Based on the small loops shown, this was likely a training flight or proficiency check. It can be assumed the aircraft was placed into an intentional stall for training or VMC demo, but quickly departed controlled flight for an unknown reason. It was very windy in Massachusetts (up to 50 mph at altitude) and wind shear may have also been a factor.

According to online aviation blogs, those who knew the pilots say that two of the fatally injured occupants were experienced senior instructors.

https://www.flightaware.com/live/flight/N7345R