The 12-year-old Adriana was shot to death at a petrol station in Botkyrka on 2 August.
According to information, the attack was about a drug conflict in the Botkyrka network, but the girl was shot by mistake.
The target was in fact people in bulletproof vests, according to information to SVT News.
It was on Wednesday that the man in his 20s was arrested on suspicion of a serious gun crime.
Circumstances led prosecutors over the weekend to request that the man be arrested for the murder of Adriana.
The degree of suspicion is suspect for probable cause.
Was previously arrested in the investigation
The man who has now been arrested is the same man who in December 2020 was arrested in the murder investigation on the lower suspicion level, and who was also released then.
The suspicions regarding attempted murder are about what the police believe is that the shots were intended for someone or some others who were at the crime scene.
The police state that at present they cannot provide any further details either regarding the murder investigation or the investigation regarding a serious gun crime.
Two have previously been arrested
The murder was noticed and several residents in the area have said that they want to move away from Botkyrka.
Earlier, two people were arrested in the murder case.