A man believed to be in his 30s died after being shot outside the Marriott Hotel in Old Shire Lane, Waltham Abbey, at 09:45 GMT on Tuesday.
Det Ch Insp Marina Ericson said the gunman was "waiting for the victim in the car park" and shot him before chasing him on foot.
A ballistics expert has been brought in to examine the scene, the force said.
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The suspect was seen getting into a dark-coloured car being driven by an accomplice following the shooting, Det Ch Insp Ericson said.
No one has yet been arrested.
Police said a key witness was an "innocent member of the public" whose car was flagged down by the victim following the shooting.
The man was driven to the Volunteer pub, half a mile away from the hotel, where paramedics tried to save him before he died.
A post-mortem examination will be taking place on the victim's body later.
A fatal shooting outside a hotel in Essex was a targeted attack on the victim, police have revealed.