Updated at 5:09 p.m.
A statement from the District Attorney's Office confirms "investigators believe that the individuals involved in this afternoon’s multiple stabbing downtown are known to one another and that at least some of those individuals had a connection to a case in Suffolk Superior Court."
The D.A. will not identify the case to the protect the court proceedings. A homicide prosecutor has been assigned and was at the scene, and is in close contact with police, the statement said.
Updated at 4:36 p.m.
The four victims were coming back from superior court on a separate case when the stabbings broke out. Police say they all know each other and it was part of the same incident, but did not know the motive for the violence.
An ambulance responded to a report of stabbings at 73 Tremont St (the call came in as 1 Beacon St). En route to the hospital, the ambulance came across another victim at 155 Mass Ave. All the victims are in area hospitals, with the man from Mass Ave. in critical condition, police said.
Nobody has been taken into custody, according to an officer at the scene.
There's at least a dozen police gathered on Tremont Street. Green markers have been placed where the stabbing occurs, and the sidewalk is blocked off.
Traffic is also closed on Tremont between Bromfield and School streets.
Original report, 4 p.m.
Multiple people were stabbed on Beacon Street and Mass Ave. today, with three currently in surgery.
The most serious-sounding injury, occurred at 155 Mass Ave. with reports that the victim tried to drive himself to the hospital. He's in critical condition, reports say. Police also responded to other victims on 1 Beacon St., near the Omni Parker House.
A fourth victim was found covered in blood in Downtown Crossing, and is said to have walked into a hospital. The stabbings all happened within minutes of each other just before 2 p.m.
Boston.com reports the police have a suspect in custody and he's being questioned by homicide detectives.
This story will be updated as more information becomes available.