A St. Paul man deliberately rear-ended a motorcyclist at highway speed last month with the intent of injuring or killing his ex-wife's boyfriend, but it turned out he hit the wrong guy.

Timothy Lee Biby, 45, admitted to authorities that he rammed a teenage motorcyclist as he drove west on 185th Street in Credit River Township around 11 p.m. on April 29, then took off. Biby said he had seen a man leave his ex-wife's condo in Lakeville on a motorcycle and believed it was her boyfriend.

He followed the motorcycle for several miles before running it down near the intersection of Hobby Hills Trail, according to charges of first-degree premeditated attempted murder and second-degree assault with a dangerous weapon inflicting substantial bodily harm filed last week in Scott County.

"I tried to kill your boyfriend," Biby wrote in a letter to his ex-wife. She provided that letter to authorities. "I saw a guy leave on a bike and I lost it. I hit him with my car. Turns out he was a high school kid."

The motorcyclist, Grant Skluzacek, 18, suffered a fractured wrist and gashes that required stitches. He is expected to fully recover.

According to the charges, Skluzacek left a friend's home in Lakeville around 10:45 p.m. and noticed a vehicle behind him as he entered a roundabout at 185th Street and Kenrick Avenue. Skluzacek headed west on 185th and the vehicle remained four to five car lengths behind even though he was traveling below the speed limit and there was plenty of room to pass.

Skluzacek sped up to 55 miles per hour after passing a neighborhood near Judicial Road. He noticed the car's lights go off and figured the driver had turned off. Seconds later, the headlights came back on, the driver revved the engine and struck Skluzacek's motorcycle.

Deputies noticed there were no tire or skid marks to indicate Biby made any attempt to avoid a collision. They also found a piece of Biby's 1999 blue Honda Accord stuck in the rear wheel of the severely damaged motorcycle.

Investigators confronted Biby at his St. Paul home about a week after the crash, and he declined to say why a piece of his vehicle was found at the crash site.

On May 4, Biby's ex-wife showed authorities a handwritten letter he sent her. In the letter, Biby stated he had driven by her condo in violation of a restraining order hoping she would be outside with her dog. That was when he saw a motorcyclist leaving and followed him.

"I hurt an innocent kid," the letter said. "I can't live like this. At least I finally quit smoking."

Authorities returned to Biby's St. Paul residence that night and he confessed.

Biby remains in the Scott County jail in lieu of $500,000 bond. His next court appearance is scheduled for July 23.