Her live-in boyfriend, who is also the baby's father, says they had gotten into an argument and she just never came back home from work.
A search warrant ABC15 has obtained indicates he may know more than he is letting on.
Phoenix police are now calling the man a "person of interest" because he lived with her, but they stress he is not a suspect in the case.
The court documents state in the days leading up to May 10, Mustafa confided in her sisters that she was afraid of her boyfriend. She was planning to take her baby, leave and get an order of protection against him.
Court documents state her boyfriend was allegedly calling her repeatedly at work with accusations of cheating, and even threatened to kill her.
After she failed to show up at work and seemingly vanished without a trace, court records state police picked the locks and made entry into Mustafa's home and searched the house but did not find Mustafa.
Officers did find her purse which contained her wallet, social security card and credit cards in plain sight. Her cell phone was discovered on the bathroom floor between the tub and toilet.
As they were investigating, authorities said her boyfriend arrived home and told police she left after a verbal argument, but didn't take her Nissan Cube because it had a flat tire. Court records state police did not observe a flat tire on the vehicle.
On May 11, the Department of Child Safety called Phoenix police for assistance on a welfare check. Mustafa's family contacted DCS to check up on the baby.
Officers greeted the boyfriend at the front door and confiscated a loaded hand gun. He told officers he had to clean the front room of his house because the dog had defecated and urinated in the home. He also allegedly told police his daughter had bed bugs so he had to use a cleaning solution to get rid of them from the mattress and linen.
DCS investigators decided to remove the child from the home.
On May 15, court records state detectives spoke to the boyfriend's sister who stated her brother was acting "paranoid" and made statements she found concerning, such as "I took it to far" and "I can never unsee the things I saw."
Court records indicate the boyfriend told his sister he got into an argument with Mustafa and she had attacked him first.
That same day a search warrant was served at the couple's home near Cave Creek and Deer Valley roads. In Mustafa and her daughter's room court records state police found pillow cases and bed sheets "which contained a small amount of possible blood stained material."
In the same bedroom "luminol was used during processing and sprayed on the walls. The luminol reacted indicating a positive response to blood or other biological matter."
Court records state the boyfriend invoked his rights and refused to be interviewed.
The search warrant states investigators are requesting the boyfriend be "compelled to provide his (phone) swipe code in efforts to locate Christina Mustafa."