Feb 14. 3:20 AM PT -- Guillod's rep tells TMZ, "David Guillod vehemently denies these allegations and is fully cooperating with the investigation as he did in 2012. He looks forward to clearing his name and the truth coming out."

The rep goes on, "In 2012, the LAPD investigated this claim and closed their investigation after witnesses contradicted Ms. Barth's statements and a saliva DNA sample collected came back as a positive match to Danny Cusumano, Ms. Barth's boyfriend, at the time, which she was having an affair with while she was married. Ms. Barth is now married to Mr. Cusumano and the truth is just starting to become clear."

8:19 PM PT -- The warrant says just after the alleged incident a DNA sample was taken that revealed the DNA on Jessica's hickeys was that of her boyfriend and not Guillod or her husband.

Hollywood producer David Guillod -- who's been accused of sexual assault by at least 4 women, including actress Jessica Barth -- is now under the microscope of investigators ... TMZ has learned.

According to legal docs ... a warrant's been issued to collect the DNA of the "Atomic Blonde" producer in connection with claims made by Barth that Guillod drugged and raped her in 2012.

In the docs, the LAPD detective handling the case says Barth claims she went to dinner with Guillod and a friend, drank a lot of wine, began feeling drowsy and can't recall anything after that. She says the next thing she recalled was coming to in her car with Guillod standing outside the vehicle and yelling at her.

She went to the hospital for a rape kit and the exam revealed a bruise on her left thigh, a bruise on her forehead and potential saliva on her breast and neck.

She says she had hickeys on her neck and asked Guillod if they had sex and he said no, but said they did have a makeout session.

The docs make it clear ... the LAPD has re-opened the investigation. The initial allegations were investigated but the case was closed in 2014. Cops say it was re-opened after "new allegations" surfaced. Cops also say they never collected a DNA sample from Guillod, so they are looking to do that now.

Guillod stepped down as co-CEO of Primary Wave Entertainment in November after Barth went public with accusations. Shortly after, 3 more women came forward with similar stories of being drugged and raped.