They were being chased away from MIT where they became involved in at least one incident. Shot and killed a MIT policeman. Then they stole that vehicle they were driving around in for about an hour.
The car they drove in for an hour was a black Mercedes SUV that they hijacked and supposedly forced the driver to drive them around city for an hour. They dropped him at the doubletree hotel according to person that reported SUV stolen. And the chase was on.