avid cyclist

Man Identified as Suspect in Irvine Bike Path Slaying

A 37-year-old man was in custody on Thursday suspected in the fatal stabbing of another man on a Irvine bike path last month, police said.

Dennis Thomas Monson Jr. was arrested on unrelated charges on Jan. 19, the same day 51-year-old Sidney Siemensma was stabbed to death while on a bike path adjacent to the 405 Freeway near Irvine Center Drive, according to a press release by the Irvine Police Department on Wednesday.

Monson, described by police as a transient, was taken into custody on suspicion of possession of child pornography, Irvine police said. Since his arrest, police continued to investigate the homicide, including submitting evidence for forensic testing, and identified Monson as the suspect in Siemensma's death. The case has been submitted for criminal charges to the Orange County District Attorney

Officials said Monson and Siemensma knew each other and got into an altercation while on a bike path behind the Los Olivos residential community.

Monson allegedly stabbed the victim repeatedly before he fled the scene.

On the morning of Jan. 19, police responded to reports of a bleeding man from a joggers and passing motorists. When officers arrived, they found Siemensma, next to a bicycle on the path. He was pronounced dead at the scene.

Siemensma was an avid cyclist and a stay-at-home dad to a 10-year-old and 14-year-old, according to his wife.

Monson was being held Thursday in lieu of $50,000 bail and is scheduled to appear in court on March 7.

Contact Us