PC Alex Ayre, 24, is understood to have jumped in front of a train near Branksome, last Friday morning.
The police officer, who joined the force in June 2022, was being investigated for gross misconduct in relation to his behaviour while off-duty and had been suspended prior to his death, Dorset Police have confirmed,
The force has since referred itself to the Independent Office for Police Conduct over its handling of the matter.
Dorset Police Chief Constable Rachel Farrell said: “Prior to his death Alex was the subject of a gross misconduct investigation in relation to behaviour off duty and was suspended from duty.
“It is important to note that suspension is not a presumption of wrongdoing, and the misconduct investigation was in the very early stages.
“As is mandatory in these circumstances, a referral has been made to the Independent Office for Police Conduct (IOPC), and we welcome any transparent review.”
His family issued a tribute to Alex, 24, who they have said was “a much-loved son, grandson, big brother, little brother, nephew, cousin, best friend and such an important person to so many people”.
They said: “You were always there for people, always happy to help, always thinking about how other people were feeling, and always someone people knew they could turn to when they needed you.
“You were the life and soul of the party, the cheeky one who could make absolutely anyone laugh. You brought so much laughter, warmth and personality wherever you went.”