Haddad, 16, was found stabbed to death late on Friday outside a block of flats in Södertälje, 40 kilometres south west of Stockholm.
The suspect has a history of mental illness. The results of an evaluation of his psychological state at the time of the killing are expected to be ready in four weeks’ time.
The girl was found dead with multiple stab wounds in the residential area of Rosenlund at around 11pm on Friday night.
The suspect was arrested near the crime scene following a tip off from a witness.
Norba Haddad lived in another part of Södertälje and was visiting the Rosenlund residential area. She was outside when she was attacked and stabbed repeatedly.