Heinrich says he saw Jenkins strike Fiore and that she felt compelled to hide one of her phone lines behind her husband's back because he would go through her text messages at night.
As recently as a month ago, Heinrich tells PEOPLE exclusively, Fiore confided that she was "in over her head" and didn't know how to escape her relationship with Jenkins, a millionaire real estate developer.
Heinrich says he personally saw "Ryan punch her in the arm with enough force to push her into a pool. That was the time he was arrested," he said. "I was there and watched it." (Jenkins was charged with misdemeanor domestic violence and had a court date in December.)
Today, Jenkins, 32, remains at large and is believed to have crossed the border into his native Canada. The mutilated remains of Fiore, 28, were found last weekend in a trash receptacle in Orange County, Calif.
Jenkins JealousHeinrich met Fiore about four years ago, when he worked at a nightclub at the Hard Rock Hotel in Vegas. We "were together on-and-off for about a year and a half in 2006, 2007," he says. "We were engaged about five months, [but] when push came to shove we realized it wasn't going to work out but we were still friends."
The violent poolside incident between Jenkins and Fiore, Heinrich recalls, came after Jenkins "was just drinking all day long." He says Jenkins also didn't like the fact he and Fiore were talking. "Then I saw them and they were yelling, exchanging words by the edge of the pool. Then he hit her and she went right into the water fully clothed. Her phone, purse, everything," Heinrich says.
Jenkins, says Heinrich, "was just so, so, so jealous. He would go through her phone every night. I think she may have even had a third phone but I'm not sure."
Describing Fiore as an independent type, Heinrich says he was surprised when, about a month ago, "she made a comment that was really weird for her. She said, 'I'm in over my head' and 'I don't know how I can get out.'"
Was she scared? "Oh, 100 percent," he says.