Four suspects in total were involved in the attack. Officer Robert Rueca confirmed to Fox News Digital that the other three suspects have been detained.
The stabbing – which police described as "unprovoked," according to FOX San Francisco – took place on a Muni bus at around 4:30 p.m at Stockton and Sutter streets.
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Four juvenile suspects in total were involved in the stabbing on a San Francisco Muni bus. (FOX 2 San Francisco)
The suspects assaulted and stabbed the 15-year-old victim. All of them were minors.
The teenage victim sustained life-threatening injuries but survived the attack.
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The teenage stabbing victim sustained life-threatening injuries is recovering at a local hospital. (FOX 2 San Francisco)
Police did not release information about the victim's condition but confirmed to Fox News Digital that he was recovering.
Officer Robert Rueca announced the 12-year-old suspect's arrest on Twitter on Tuesday.
The 12-year-old stabbing suspect was charged with attempted murder and sent to a juvenile facility. (FOX 2 San Francisco)
"Thanks to witnesses & @SFPDCentral officers involved in saving victim's life and apprehending suspect," he wrote.