Detective Inspector Iain MacPherson, from the Beds, Cambs and Hertfordshire Major Crime Unit, said: "Our thoughts are with the family and friends of the three people who have sadly died.
"Hertfordshire Fire and Rescue Service were already in attendance as there was a fire at the address.
"Officers and paramedics attended but sadly two women and a man were pronounced dead at the scene.
"Detectives are investigating the circumstances and forensic officers and the fire investigation team are at the location as part of this."
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