In Longmont, police said officers responding to a call shot a postal worker in front of the neighborhood mailboxes. The worker died on the scene.
Witnesses told police the suspect was wearing dark clothes, a hoodie and a blue mask when he ran, according to Longmont Deputy Police Chief Jeff Satur.
The US Postal Inspection Service has joined the investigation. The postal service said there is no additional information to post.
The suspect, another postal worker, died of an apparently self-inflicted gunshot wound, according to Lisa-Anne Culp, a spokeswoman for the Memphis FBI office.
The authorities have not disclosed the names of the victims.