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   WATERTOWN, Mass. (AP) - Police say one of two suspects in the shooting of an MIT police officer is dead and a massive manhunt is underway for another, who is tied to the Boston Marathon bombing.

   Shortly after the MIT officer was shot Thursday night, police got a report of a carjacking in Cambridge, just outside Boston.

   Police say of the at-large suspect, "We believe this to be a terrorist."

   The FBI is investigating whether the fatal shooting of a campus police officer at the Massachusetts Institute of Technology and gunfire and explosions in a nearby town are related to the Boston Marathon bombings.

   A Massachusetts State Police spokesman said early Friday that one person suspected in the gunfire and explosions has been accounted for and one is at large.

   The FBI said it is working with local authorities to determine what happened.

   The MIT shooting on the Cambridge campus Thursday night was followed by reports of violence in nearby Watertown, about 10 miles west of Boston.

   State police spokesman David Procopio said there is a "strong possibility" the incidents are related.

   The MIT officer had been responding to report of a disturbance Thursday night when he was shot multiple times, according to a statement from the Middlesex district attorney's office and Cambridge police. It said there were no other victims.

   In Watertown, witnesses reported hearing multiple gunshots and explosions at about 1 a.m. Friday. Dozens of police officers and FBI agents were in the neighborhood and a helicopter circled overhead.

   State police spokesman David Procopio said, "The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers."

   Boston cab driver Imran Sais said he was standing on a street corner at a police barricade across from a diner when he heard an explosion.

   "I heard a loud boom and then a rapid succession of pop, pop, pop," he said. "It sounded like automatic weapons. And then I heard the second explosion."

   He said he could smell something burning and advanced to check it out but area residents at their windows yelled at him, "Hey, it's gunfire! Don't go that way!"

   MIT said right after the 10:30 p.m. shooting that police were sweeping the campus in Cambridge and urged people to remain indoors. They urged people urged to stay away from the Stata Building, a mixed-use building with faculty offices, classrooms and a common area.

   Hours later, MIT, which has about 11,000 students, said the campus was clear but the shooter was still on the loose.

   Flooding continues to be a problem in the St. Louis metro area as rain-swollen creeks remain out of their banks.  

   Now the National Weather Service is warning that the Mighty Mississippi will likely over-spill it's banks in the next few days.  A flood warning has been issued for communities along the river from Canton, Missouri -- north of Hannibal, to Chester, Illinois.  That warning includes the riverfront in St. Louis.  

   Officials say the Mississippi will rise above flood stage by Friday evening.  It's expected to crest at around 39.4 feet by Tuesday morning.  

The National Weather Service has lifted a tornado watch for St. Charles County, St. Louis County and St. Louis City.

Variable clouds and becoming windy with rain and a few thunderstorms - possibly severe this afternoon. Storms may produce large hail and strong winds. High 67F. SSW winds at 5 to 10 mph, increasing to 20 to 30 mph. Additional rainfall may reach one inch.

Tonight:

Cloudy early with some clearing expected late. Low 36F. Winds W at 15 to 25 mph