A modern-day duel between rivals was played out in dark SUVs racing on Interstate 90 at more than 100 mph, weaving recklessly through traffic — a screaming toddler in one vehicle and a vengeful man in the other, prosecutors say.

The motive behind the chase last week that ended when both vehicles crashed near Issaquah wasn’t road rage, as the Washington State Patrol, prosecutors and even witnesses initially believed.

It was jealousy, prosecutors say.

The man who allegedly initiated the high-speed chase, Desi C. Beltran, 29, of North Bend, has been charged with one count of second-degree domestic-violence assault and two counts of second-degree assault. He is being held in King County Jail in lieu of $250,000 bail and is to be arraigned Feb. 4.

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The other driver, Hugo Yanez, 32, of Bellevue, was arrested on unrelated warrants after the chase, but has not been charged in the incident. A spokesman for the King County Prosecuting Attorney’s Office said a charging decision will be made once the police investigation has been forwarded to them.

According to documents from prosecutors and police investigators, the woman at the center of the conflict is a 27-year-old Cle Elum resident with a 2-year-old son.

She had spent Jan. 15 at a casino with Yanez, whom she described to police as a friend, prosecutors say. But Yanez says they were romantically involved.

At the casino, the woman told Yanez she needed to pick up her son from her mother’s Cle Elum home and asked him to drive her in her Ford Freestyle, according to police.

Yanez agreed, but when they arrived, the woman told him to “get out of the car and lay low” until she had picked up her son because she had a contentious relationship with her mother, according to the State Patrol.

Her mother, however, came outside with the child, saw Yanez and did not like the looks of him, investigators wrote.

According to a report she filed with the Kittitas County Sheriff’s Office a short time later, the older woman initially told police that Yanez had “ripped” her 2-year-old grandson from her arms. She later told a deputy that while that was untrue, he did make her “feel very uncomfortable.”

Police told her that because the boy’s mother had custody of the child, they would not investigate further, according to a report from the Sheriff’s Office.

The grandmother then called Beltran, according to court documents.

In an interview with the State Patrol, Beltran said he immediately believed his girlfriend had been cheating on him.

Beltran told investigators he drove onto the freeway near North Bend and waited on the inside shoulder in his Ford Explorer until he saw his girlfriend’s SUV pass, then began to follow it, according to charging documents.

According to police, Yanez was behind the wheel of the woman’s Freestyle. She said that in his efforts to lose Beltran, Yanez wove through traffic, veered across lanes and drove up to 120 mph.

The woman said she was terrified and climbed into the back seat to comfort her son, who was screaming, “You’re scaring me!” according to the report.

Witnesses told police the Explorer repeatedly rammed the smaller SUV and that both cars nearly clipped other vehicles multiple times.

“I anticipated an accident,” one witness later told police.

Another witness told police: “The other traffic that was on the freeway at that time on I-90 was hitting their brakes and doing everything to stay away from them.”

Beltran claimed he rammed the other vehicle only when Yanez jammed on his brakes, according to the charging documents. However, several witnesses told police it appeared the Explorer was trying to run the smaller SUV off the road.

It looked like “just absolutely insane road rage,” said one witness who called 911 and later talked to State Patrol investigators.

Once both vehicles crashed in the median near the West Lake Sammamish Parkway exit, Yanez got out of the woman’s SUV and ran off, according to police and prosecutors.

After he was tracked down by a K-9 unit and treated for dog bites, he told police he fled because he was frightened of Beltran and because there were two misdemeanor warrants out for his arrest.

According to police, Yanez was hesitant to describe his relationship with the woman. He said they were friends, but later said they had been romantically involved, according to the police reports.

Christine Clarridge can be reached at cclarridge@seattletimes.com or 206-464-8983.