“There was a small, green object by the roadside on Sköndalsvägen,” Ulf Lindgren, an information officer with the Stockholm police, told the TT news agency.
The area was sealed off while bomb technicians retrieved the device for further investigation.
On August 11, the 4-year-old was seriously injured when she discovered a homemade bomb hanging from a shed guttering close to the sand box in the school playground.
A 15-year-old boy was arrested the following Monday, under suspicion for placing the device in the gutter. He will remain detained until September 1st.
During last week, two additional explosive devices were discovered in the same area – one found hanging from a goal on a football field and another found near a playground, only metres away from playing children.
A warning was issued by the police that the public should beware unidentified objects wrapped in green tape and that any new discoveries should be reported immediately.
Police subsequently arrested a second suspect, an 18-year-old man, suspected of working together with the 15-year-old, on Friday.
After a hearing on Saturday he is now remanded into custody on probable cause, the stronger level of suspicion related to aggravated assault.
Prosecutor Åsa Andersson will not elaborate on the evidence against the older teenager.
The 18-year-old’s lawyer says he denies the crime, according to reports in daily newspaper Aftonbladet.