Police have identified a “person of interest” in custody on unrelated allegations as a suspect in the killing of an Irvine man on a bike path last month.

The suspect, Dennis Thomas Monson Jr., a transient who frequents the bike path near the Los Olivos neighborhood, was arrested the evening that Sidney Siemensma, 51, was stabbed to death, the Police Department said in a news release Wednesday.

Siemensma’s body was discovered about 7 a.m. Jan. 19 on a bike path that runs adjacent to the southbound side of the 405 Freeway south of the 133 Toll Road, according to police.

Dennis Thomas Monson Jr. (Courtesy Irvine Police Department)

Authorities received calls from passersby who thought a bicyclist on the path had been injured, Irvine police spokeswoman Farrah Emami said at the time. But when emergency crews arrived, they determined the man was dead, she said.

Police said Wednesday that a man with whom Siemensma was acquainted was “quickly identified” as a possible suspect the evening of Siemensma’s death. According to the news release, police believe Siemensma was stabbed repeatedly during an altercation between the two.

Monson, 37, was contacted by police on the same bike path where the stabbing had occurred earlier.

Officers also discovered what they believed to be child pornography on Monson’s cellphone. He has been in custody on child pornography charges since Jan. 19, authorities said.

Detectives continued their investigation and identified Monson as the suspect in the stabbing, the department said.