A deadly case of jealousy left an 18-year-old Fontana man dead when the boyfriend of a female co-worker ran the 18-year-old down as he crossed a street Wednesday evening, police said.

Cristian Dominguez-Aguilar was less than a block from his house when police say John Nieto, 20, ran the 18-year-old down because Nieto believed Dominguez-Aguilar was having an affair with the mother of Nieto’s child, according to police officials.

“He knew they worked together and he knew that she would give him a ride home,” said Sgt. Kevin Goltara, spokesman for the Fontana Police Department. “I think (Nieto) thought something was going on between them but according to her, there was no affair.”

Elisabeth Mancilla, also 20, of Rialto was arrested as well because police say she witnessed the attack and instead of calling the police, she picked up the fleeing Nieto and drove him home.

“I can’t believe this,” said Liliana Dominguez, Dominguez-Aguilar’s cousin. “All I can think about him right now is his smile. He big, happy smile. He was a really happy young man and I can’t believe he’s gone.”

Dominguez said her family has already suffered many losses over the years and the senseless death of her 18-year-old cousin has left the close-knit family reeling.

“He lost his mom at a young age so he had to grow up without a mom but earlier this year he lost his grandpa and that was really hard,” Dominguez said adding that her cousin’s father was in Mexico at the time of the fatal attack. “We’ve been through a lot.”

Dominguez said the 18-year-old was living with his older brother, Armando Dominguez and his grilfriend. He also has a younger brother, but he is in Mexico, she said.

“He was a good young man,” she said. “He was going to college and going to work. He was a good person.”

Around 7:15 p.m., police say Nieto, who lives in San Bernardino, was waiting for Mancilla to drop Dominguez-Aguilar off at the 7-Eleven in the 17700 block of Foothill Boulevard.

When Nieto saw Dominguez-Aguilar crossing the street, Goltara said Nieto accelerated his white 2003 Chevy Silverado toward the 18-year-old. He missed him the first time and Dominguez-Aguilar ran back toward the 7-Eleven in an effort to avoid the large truck, officials said.

Nieto caught up with the fleeing man as he ran toward the back of the business and struck Dominguez-Aguilar, Goltara said. He was going so fast that Nieto lost control and struck the building disabling the truck, Goltara said.

The 20-year-old jumped out of his truck and ran off, according to authorities.

Mancilla then drove down the street, picked up Nieto and drove him to his San Bernardino home, Goltara said. She then drove home to Rialto but never called for help.

“The girlfriend is in the car watching this the whole time and she didn’t render aid or check on her co-worker,” Goltara said Thursday.

At some point, Nieto drove to to Mancillas home and that’s where investigators found the couple and their child Thanksgiving morning, police said.

Nieto was arrested on suspicion of murder and Mancilla was arrested on suspicion of being an accessory. Both were booked into West Valley Detention Center in Rancho Cucamonga. Their child was left with family members.

“This is really an unfortunate situation because (Dominguez-Aguilar) lost his life essentially over nothing and both of these young parents have ruined their lives forever,” Goltara said. “And their child is now without their parents. It’s just a very sad case.”

The family has started a GoFundMe account to help pay for burial costs.

Fontana police ask anyone with any further information to the case to call Detective Jason Coillot at 909-350-7700, in reference to case #17-21044.