A lot of police work and collaboration went into the case, but it's interesting to note the role DNA evidence played here. Im had apparently been stabbed in Columbia's Maryland Avenue parking garage (map), placed in a car trunk and set ablaze. Despite the fire, a lot of DNA evidence was recovered, according to the MUPD press release.
"The knife, along with additional forensic evidence, including blood, hair and touch DNA, was collected at the crime scene."
The MUPD provided this useful explainer for "touch DNA":
"Touch DNA refers to the DNA that is left behind from skin cells when a person touches or comes into contact with an item. Human beings shed tens of thousands of skin cells each day. These skin cells are transferred to every surface our skin contacts. When a crime is committed, if the suspect deposits a sufficient number of skin cells on an item at the scene, and that item is collected as possible evidence, touch DNA analysis may be able to link the suspect to the crime scene. Touch DNA has been successfully sampled from countless items including gun grips, steering wheels, seat levers, door handles, eating utensils, luggage handles, and countless other items."
It sounds like quite a lot of evidence, but MUPD says they followed "at least 300 leads" and checked approximately 60 DNA samples without turning up any matches. The case stayed under active investigation for 8 years while MUPD pursued these leads.
Timothy Hoag's apparent suicide at the Fifth and Walnut parking garage in Columbia happened late this summer, but MUPD never checked for a DNA match until December 21 this year when a witness identified Hoag as a suspect in the case. MUPD says they found a match in all three samples: blood, hair, and touch.