Afterward, they went to Stone's apartment at 1205 Baker Place, off Key Parkway near Frederick Towne Mall.
Martyak said Stone and Brall talked about a .40-caliber handgun that belonged to Stone's roommate, who was not home. Then, they went to a rear bedroom to look at it, Martyak said.
As Stone held the gun, it went off, firing one round into Brall's chest, Martyak said.
Stone was being held at the Frederick County Adult Detention Center on Thursday afternoon. His bond was $15,000.
News of the shooting death stunned Kaplan College, formerly Hagerstown Business College, said Dean of Student Affairs Lisa Copenhaver, who spoke with Brall in her office on Wednesday.
"I'm still in shock," she said Thursday afternoon, describing Brall as "a really pleasant young man."
In January 2006, Brall earned an associate degree in business administration from Hagerstown Business College, said Lisa Boice, a dean at the college.
This year, the school started offering four-year degrees. Boice said Brall came back to get a bachelor's degree in business administration.
As he did last time, Brall was going to live on campus. He had moved into an apartment, Copenhaver said.
An employee at Chambersburg Area Senior High School said Brall graduated from the school in 2003, but she wasn't able to find someone who could talk about him for this story. A yearbook listed him as a manager for the football team.
Stone, Brall and about four or five other people were in Stone's apartment, according to Martyak.
A few minutes after they arrived, Stone and Brall went to look at Stone's roommate's gun. Martyak said the roommate legally owned the gun, which was registered.
There was no dispute between Stone and Brall, he said.
Others in the group heard the conversation about the gun, but were not in the same room when the shooting happened.
Police said in a news release that Stone was hit once in the upper right side of his chest.
Police officers administered first aid at the scene, but emergency medical workers later determined that Brall was dead, the news release says.
His body was taken to the state medical examiner's office for an autopsy.
Stone, who called 911, cooperated with police, Martyak said.
A woman who identified herself as Stone's grandmother said Thursday afternoon that she didn't know many details about what happened.
Frederick attorney Thomas Sinton, who previously represented Stone, didn't know about the shooting until he was contacted by a reporter.
Maryland's court record system shows that Stone was sentenced to four years in jail in August 2006 on a conviction of second-degree assault.
The jail time was suspended, except for about two weeks that he served in 2005.
Stone also was placed on two years of supervised probation, court records indicate.