The department says the escape happened about midnight Friday but department officials weren't informed until Sunday.
A company called Prisoner Transport Services of America had been hired by the state to return Ali to Delaware.
Ali was convicted of attempted murder in Delaware in 1995, but was sent to California under a prisoner exchange agreement.
Police describe Ali as:
- 43 years old
- Black hair and brown eyes
- Stands 5'10"
- Weighs 165 pounds
- Wearing white T-shirt and khaki pants
Officials suspended all interstate transport of Delaware prisoners until they figure out how Ali escaped.