The gunman – said to be wearing a “black skull mask” – broke into the home shortly after midnight on Tuesday and appeared to know the layout of the property, police said.
The “horrific” crime unfolded in Pasco County, Florida after midnight on Tuesday, October 1.
According to Pasco County Sheriff Chris Nocco, the gunman entered the property by kicking through a door. Another woman sleeping on a sofa was awoken, but the suspect passed her and headed upstairs, he told the news conference.
Sheriff Nocco said the suspect moved to the bedroom where the victim was in bed with two children under the age of 12, turning the light on.
She reportedly sat up and said “don’t shoot me” before the assailant shot at her once.
She fell out of the bed and the gunman shot at the woman again striking her, according to police.
The woman was taken to hospital but died a short time later.
The suspect is believed to have fled in a vehicle before police arrived.
Sheriff Nocco said: “For these young kids, I can imagine they were out last night trick or treating.
“I can imagine they went to bed a little bit later like all kids did last night.”
He added: “To be woken up to have a suspect walk in, turn that light on and shoot the person in the bed with them, it’s horrific, that’s the only word I can think of.”
The suspect knew “exactly” where he was going and who the target was, Nocco added. He said: “It clearly looks to us like this was a targeted hit.”
Police urged locals to come forward with any information which could be related to the case including CCTV footage from homes and doorbell cams.
The man was reported to be around 5ft 10 inches with a heavy build wearing dark clothing.
Anyone with information is asked to submit tips to the PSO Crime Tips Line at 1-800-706-2488 or report tips online at PascoSheriff.com/tips.