Man Who Cops Say Fatally Shot Firefighter Released After Questioning No charges were filed but the investigation is ongoing, police said.

 -- A man who opened fire on two firefighters carrying out a welfare check at a Prince George’s County, Maryland, home, killing one and wounding the other, was released today after being questioned, police said.

John Ulmschneider, a 13-year veteran firefighter, died after he and firefighter Kevin Swain entered a home for a "check on the welfare" call and were shot at by someone inside, the Prince George's County fire department said.

Ulmschneider, 37, was hospitalized in extremely critical condition with a gunshot wound to the upper body, the fire department said. He died at Med Star Southern Maryland Hospital Center. He is survived by his wife and 2-year-old daughter.

Swain, 19, a volunteer firefighter who was shot four times, underwent surgery at the Shock Trauma Center in Baltimore. Surgeons completed the operation early this morning and Swain remains hospitalized in serious but stable condition, officials said.

The incident began around 7:30 p.m. Friday when firefighters responded to a "check on the welfare" call in Temple Hills, after someone had reported that they could not contact another family member who lives in the home, the fire department said.

After no one answered the door, firefighters entered, and someone fired at Ulmschneider, Swain and the family member who had called 911, the fire department said.

The family member's injuries are not considered life-threatening, the Prince George's County Police Department said.

Officials said today that two other Morningside Volunteers members were injured while seeking cover during the shooting -- one firefighter sustained a knee injury and another sustained a jaw injury. Both were treated at a hospital and released early this morning.

The suspected shooter, whose identity was not released, was taken into custody and was released after being questioned, a police spokesman said. Since no charges have been formally filed, the shooter could not be held, the spokesman said, adding that the investigation was ongoing.

Mark Brady, Public Information Officer for Prince George’s County Fire, said the suspected shooter and the 911 caller are brothers. The brother who called 911 told authorities his brother had been having trouble with his blood sugar and recently blacked out, and he was concerned because his brother wasn’t answering his phone or the door, Brady said.

ABC News' Sarah Shales contributed to this report.