Officers first responded to a call about "shots fired" at about 5 p.m. coming from an apartment in the 9900 block of 12th Avenue West.
When they arrived, police found a dead woman and an injured man inside the apartment. The woman had been shot to death and the man had been stabbed.
Also inside the apartment were two children, though neither was injured.
The wounded man was taken to Providence Medical Center and his current medical status is unknown, according to Everett police.
The kids were taken into temporary protective custody.
A neighbor named Kaitlyn said she was home watching TV when she heard a loud "boom" Thursday evening. It wasn't until later that she realized what had happened.
"It's scary. It's really scary," she said. "I don't know what to think."
Detectives are investigating the bloody scene, but so far it's unclear what sparked the violence or who is responsible. Police do not believe anyone but the two adults inside the apartment is involved in the incident.