Tales of jealousy and anger
According to Gross and Leonardo's social media accounts, they are engaged.
FOX40 spoke with Montana Howland, who considers Leonardo his sister, and Misty Dawn Grasty, who grew up with Gross and used to live with him as a child when their families were both in the same sober living house.
"He was an angry person but I don't think he would take it out on other people," Grasty said.
"She has emotional issues but she would not physically hurt someone else," Howland said.
They were trying to understand how the couple could have left Cuesta for dead.
Grasty said Gross had a rough childhood but internalized his emotions.
"Like he would cut himself," she said.
She said Gross was always the odd one out, but that his fiancee was extremely jealous.
"She actually got physical with him inside of a store for looking at another female," Grasty said.
Grasty told FOX40 people who know the couple think that jealousy could have been directed at Cuesta. But Howland said he video chatted with her from Kansas just days ago. He said she mentioned Gross talking to another girl, but it was a joke.
Howland believed Gross to be the only one capable of such violence.
"Daniel has always talked about if someone pisses him off bad enough he will kill them," Howland said. "But Melissa is the only one with a car and she goes everywhere Daniel goes, so that's probably the reason she got (dragged) into it."
Howland told FOX40 he knew Leonardo owned a lot of knives, but only as collector's items. He didn't think she would ever use them to stab someone.
"I just know my sister willingly would not kill someone without someone mentally controlling her mind," Howland said.