Homeless man charged with murder in Irvine stabbing on bike path

A homeless man was charged Tuesday with murder in connection with the stabbing death of an Irvine man whose body was found on a bike path in January.

If convicted, Dennis Thomas Monson Jr., 37, could face a maximum sentence of 26 years to life in prison for the murder count, plus a sentencing enhancement for use of a knife.

Authorities allege Monson was on the San Diego Creek bicycle trail in Irvine the morning of Jan. 19 when he got in an argument with Sidney Siemensma, 51. The two were acquaintances, according to the Orange County district attorney’s office.

During the argument, Siemensma was stabbed multiple times, authorities said.

Around 7:20 a.m., a jogger reported to police that a man was injured and bleeding on the trail, according to authorities. Siemensma died at the scene, prosecutors said.

Police said they also received calls from drivers on the nearby 405 Freeway who could see Siemensma’s body and thought he might have been injured in a bike accident. A bicycle was found near his body, according to police.

Though Monson was charged with murder Tuesday, he has been in custody since the day of the killing, authorities said.

According to the district attorney’s office, an Irvine police officer found Monson near the trail and searched him. Prosecutors allege the officer found sexually explicit pictures of minors on Monson’s phone.

Monson was arrested, and separate from the murder case, he was charged Jan. 21 with felony possession of child pornography. He has pleaded not guilty.

If he is convicted of that charge, Monson could face a maximum sentence of three years in prison.

Monson is scheduled to be arraigned on the murder charge Friday.