An ex-swimsuit model who was reportedly a 2016 campaign office manager for Donald Trump allegedly shot and killed her estranged husband.

Ashley Christina Benefield (née Byers), 28, turned herself in on Wednesday, November 4, in Lakewood Ranch, Florida, after police found probable cause for her arrest in Manatee County.

After a five-week investigation, detectives in the sheriff’s office informed Benefield’s attorneys that they planned to charge her with second-degree murder for the September 28 shooting of Douglas Benefield, 59.

At the time of the shooting, the couple was separated while in the midst of a custody battle over their two-year-old daughter.

Mrs Benefield was arrested and charged with Second Degree Murder and is being held at the Manatee County Jail

Mrs Benefield told investigators that she shot Doug in defence during a "domestic argument".

But detectives say they have been unable to find evidence to support these claims.

"In the course of the investigation detectives determined Ashley shot Doug, during what she had described was as a domestic argument," the sheriff's office said in a press release.

"However detectives found no evidence that she was acting in defence when she fired multiple shots at her husband. She claimed he was attacking her, but detectives found no signs that she had been physically abused."

Ashley Benefield, 28, allegedly opened fire while husband Doug Benefield, 59, had his back towards her

An arrest affidavit revealed that Doug had his back turned when he was twice struck by a .45 caliber handgun, reports the Braden Herald.

"These things take a little bit of time," Manatee County Sheriff’s Office spokesperson Randy Warren told WFLA-TV.

"We really have to look to make sure there is no evidence she had been abused and that just did not exist in this case.

"We are looking for injuries, we are looking for torn clothing, we are looking for a sign of struggle, things that were inside that residence.

Investigators say Mrs Benefield is a former Trump Campaign Office Manager in Sarasota

"We got a warrant, we were able to go in, we were able to examine that closely.

"There was no evidence there that this was an act of defence."

County court records indicate that Ashley has on several occasions filed petitions accusing her husband of domestic violence.

"In each of these cases, it did not appear that she was being abused," Warren said.

"We could not find anything there that would have led us to arrest her husband for whatever these claims were even some involving their child."

Doug was a Navy veteran who founded a ballet startup along with his wife in Charleston, South Carolina, three years ago and they ran the company together.

But shortly after they set it up, the company was sued by dancers and choreographers who alleged their contracts were breached when they were fired just weeks after being hired.

Investigators say Mrs Benefield is a former Trump Campaign Office Manager in Sarasota, where she received $3,000 a month plus expenses, and was a Director of Florida Women for Trump in 2016.

She is said to have been tasked with managing the campaign office in the Sunshine State for the president in Sarasota and reportedly traveled on least one occasion to other states for rallies, according to Bill Warner Investigations, a sleuthing firm based in Florida.

The Washington Times reports that at the Illinois GOP Convention in May 2016, the then 22-year-old Ashley was “introduced as a ‘retired ballerina.'"

The Sun reports she was a registered Republican in Lakewod Ranch, Florida, from the age of 21, according to voter records.

Mrs Benefield is also reported to have an account at ModelMayhem.com under the name "Christina Alessia".

Mrs Benefield was arrested and charged with Second Degree Murder and is being held at the Manatee County Jail, where she turned herself in last week.