The man was arrested on Tuesday on probable-cause suspicion of murder. He denies the crime.
"The investigation is now continuing, including technical examinations, a review of mobile phones and the like. An important part of the investigation is trying to find out what the motive was for the murder. We will also conduct several interrogations with those involved," says senior prosecutor Sara Malmhester in a press release from the Swedish Prosecution Authority.
The murder victim, an 18-year-old man, was fatally shot aboard a bus at around 3 p.m. on Wednesday last week. The bus had about 20 people on board and was at a bus stop next to a school when the murder was committed.
Court documents show that the suspect was identified the next day and an arrest warrant was issued in his absence. He was later arrested and taken into custody at 5:30 p.m. on Saturday. However, police and prosecutors only announced on Monday that a person had been arrested.
The man's identity is still being kept secret by the court.
The police have conducted a large number of interviews and also secured video material, including from the bus.
The bus murder in Tyresö was one of five shootings that occurred within a few days. Four young men were killed in these shootings: three teenagers and a 20-year-old.
