Clifford Reed was sentenced to the maximum of 41 months in jail for the 1996 murder case.
In court Friday, friends told the judge the murder had taken a toll on Johnson's entire family -- particularly her father who was diagnosed with terminal cancer.
"It is so ironic through Mr. Reed's actions her father gets death and Mr. Reed does not," said family friend Vicky Fulkerson.
When Johnson failed to show up for several appointments on April 25, 1996, her estranged husband called police. Days later, her car was found in a grocery store parking lot and her wallet was found at a hardware store parking lot.
Reed's neighbor said he saw Johnson's car parked outside his apartment building on April 26 and later saw Reed drive the car away alone, court records said. Reed's roommate told officers that after Johnson disappeared, Reed uncharacteristically vacuumed the apartment and cleaned the carpets with a rented carpet cleaner.
Court records say that before Johnson vanished, Reed had told friends that he had a relationship with her and they would eventually marry.
A childhood friend said Reed seemed distraught two weeks before Johnson disappeared because she had told him their relationship was "strictly friends only," court records said.
Johnson's skeletal remains were found in 2004 by WSDOT workers along SR-410. Initially King County prosecutors said there wasn't enough evidence to charge Reed, and released him. New evidence led to his arrest in 2012.
The Associated Press contributed to this report