A woman and two children are dead following a Christmas Day incident at a Northeastern University parking garage in Boston, CBS Boston reports. Police responded just before 1:30 p.m. to the Renaissance Park Garage, where they found the three unconscious. They were pronounced dead at a nearby hospital.

"At this point, this is a death investigation," Boston Police Commissioner William Gross said at a news conference, calling it "a tragedy."

Police were in the process of identifying the three. The children are believed to have been under 5 years old based on car seats found in an SUV on the rooftop level of the garage. It was towed away by police for investigation Wednesday evening.

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Gross said he wouldn't rush to conclusions about the cause of the deaths. He said the medical examiner's office would attempt to pinpoint them.

Police haven't specified the relationship between the woman and the children.

Suffolk County District Attorney Rachael Rollins is leading the investigation.

"As a mother, it was incredibly hard, this scene in particular, where there were two young children that lost their lives today," she said. "We're going to do everything that we can to get the answers."

"On Christmas and the holiday season where many people are celebrating, it can be a challenging and difficult time," Rollins said. "I feel it imperative that we let people know that there is help."

She confirmed that it's the same garage from which Boston College student Alexander Urtula jumped to his death in May.

Several people at an MBTA station next to the garage and on a bus that was pulling into the station witnessed the incident, CBS Boston said.

Officers could be seen around the subway station looking for witnesses, later taking some away for questioning.

Benny Walker was among the half dozen passengers on the 47 bus that was arriving at the station. He told CBS Boston the bus driver saw one of the children on the ground.

"He jumped off and ran over and he checked the child and somebody yelled out 'Look out!"' Walker said.

Rollins and Gross were on-scene speaking with officers.

Resources were made available for officers, MBTA employees and any witnesses who were on scene during the tragic incident.

Boston Police Patrolmen's Association EMS Division President Michael MacNeil tweeted about the incident's aftermath:

Boston EMS are with the families experiencing this unspeakable tragedy on this holiday. Unfortunately, we know all too well that this kind of trauma leaves scars on first responders as well. We are committed to caring for our members and our brothers and sisters in the police and — Michael MacNeil (@mmacneil19) December 25, 2019

CBS Boston security analyst Ed Davis said providing mental health resources to first responders in a situation like this is crucial.

"It's extremely important," Davis said. "It gives them a chance to vent. … To maintain your health and personal relationships, it's really important for you to talk this out."