Green was smart but "a little different" and had moods that were up and down, Merz said.
Green, a Baltimore-area native, graduated from Morgan State University, where he excelled.
Chinedu Nwokeafor, a 20-year-old junior at Morgan State, said Green was an important mentor to him two years ago, when he was a freshman struggling with his course work and Green was a senior resident assistant in O'Connell Hall, the campus dorm he lived in.
Nwokeafor said he met Green one night near the front desk of the dorm. Green told him he noticed he didn't go to his classes, and asked him about his frustrations.
"He literally helped me out in everything I was doing," said Nwokeafor, who is from Bowie. "He sat there for almost two hours advising me on what I could do, what teachers I could talk to. He told me if I needed anything, I should come talk to him, which I continued to do."
Nwokeafor, who is now a speech communications major, was at the time studying engineering, and Green routinely helped him with his course work, he said. Green even took Nwokeafor along to an event held by NASA.
"He exposed me to many experiences I will never forget," Nwokeafor said.
When Nwokeafor came across a news story online on Tuesday naming Green as the alleged shooter in College Park, he "couldn't believe it," he said.
"I've only known him as very, very calm, soft-spoken, somebody who's not anything close to violent," Nwokeafor said. "I still believe he's that kind of person."
The last time the two touched base was sometime last year, Nwokeafor said.
By Wednesday, police had not said which mental illness Green suffered from, or what his motive might have been. Friends of Green did not know, either. Police did not find a suicide note.
Clinton Coleman, a Morgan State spokesman, said the university is cooperating with law enforcement to provide all records requested of them, but that he could not comment on whether Green had received mental health services at the university. College Park officials said he had not been treated for mental illness at their health care facilities.
College Park students on Wednesday said they were shocked by the crime, even as they noted a recent rash of armed robberies and the usual need to be vigilant off campus.
Some students wondered why they were not told more by the university about what happened and hoped campus police would step up patrols.
Marvin Mathew, 22, said the whole campus is mourning and thinking of the families.
"Our hearts go out to those families," he said. "It could have happened anywhere, to anyone."
Green bought his weapons legally, police said. Current law does not prevent those who seek treatment for mental illness from buying a gun unless they have been committed to a psychiatric institution for more than 30 days.
Despite his stepson being a victim of gun violence, Merz said he's not sure stricter laws would have prevented what happened, pointing out that Green was also carrying a machete.
Oa wants to meet with the parents of Rane to tell them what he remembers of the attack.
"Neal's the only one who survived it so he's the only one left with something to say," Merz added.