HOUSTON (KTRK) -- A long-time, well-known homicide investigator with the Harris County Sheriff's Office acknowledged engaging in "consensual sexual contact" with a key witness to the Aug. 28 shooting death of Deputy Darren Goforth, court documents obtained by abc13 show.The witness is the same woman -- an eyewitness to the cold-blooded killing -- who said in court documents filed last month that she had a "romantic relationship" with Goforth "during the preceding 15 months," two courthouse sources close to the investigation toldThe investigator, Craig Clopton, said in the court records that his sexual contact with the woman took place "during the ongoing criminal investigation."Harris County Sheriff Ron Hickman announced Friday that Clopton was "relieved of duty pending the outcome of our joint investigation with the District Attorney's Office," less than an hour after abc13 broke the news about Clopton's admission -- and the impact it might have on the case."This investigator's conduct was unethical and inexcusable and does not reflect the core values of the Harris County Sheriff's Office," Hickman said. "The misconduct of this individual investigator is an anomaly and does not represent the conduct of the men and women who work daily to protect the lives of the citizens of Harris County."Clopton's neighbors came to his defense Friday saying he is a loving and caring father and husband."He loves serving his community. I've always admired him for all the work that he's done. I mean, I realize that it's Harris County, but he still does a lot of work for our neighborhood. And so I just feel like it's false allegations," said Joanie Sharp.The man accused of killing Goforth, Shannon J. Miles, was arrested the day after the shooting. He was charged with capital murder and and remains behind bars.ABC-13 reporters on the scene the night Goforth was killed talked to witnesses who say they saw a woman in dressy clothing crying over the deputy's body.Other eyewitnesses said she called Goforth her "best friend," while over the body that evening.Sheriff's officers made no mention of such a witness the night of the murder. She was only disclosed in court documents weeks later.That, and this admission of a top sheriff's investigator having sex with Goforth's alleged paramour, could affect the credibility of the witnesses, according to defense attorneys who spoke with abc13. Witness credibility is key in capital murder cases -- and could mean the difference between a life sentence or death row, they said.Defense attorney Patrick McCann is not involved with this case but said that this latest development is "significant" and has "foolhardiness written all over it.""Whatever truth comes out of this, there needs to be a bias-free investigation and an appearance of a bias-free investigation," said McCann, a past president of the Harris County Criminal Lawyers Association."If you have a witness who has a personal stake in this and an investigator who has a personal stake in the witness, any investigation you have is going to be flawed from the outset."McCann said there is a possible greater conflict of interest, too."I don't know why the sheriff's office would want to be part of an investigation into the death of one of its own," he said. "I understand the impulse, but there's no way to get to an objective truth if you're going to have the agency that has an agenda do the investigation."Goforth's killing made national headlines when he was murdered. Harris County Sheriff Ron Hickman called the killing a "cold-blooded assassination" and criticized the 'black lives matter' movement."Cops' lives matter, too," Hickman said at the time. "So why don't we drop the qualifier and say lives matter."Investigators say Goforth had worked an accident scene at around 8:30pm, then went to a gas station on Telge and West road.As he was pumping gas, detectives say Miles approached Goforth from behind, said nothing, and fired multiple shots at the deputy. Once he fell to the ground, authorities said Miles fired more shots into Goforth. Goforth was pronounced dead at the scene.