Prosecutors decided that "the actions of the officers in using deadly force were justified," Howard State's Attorney Dario J. Broccolino said in memo sent to police Friday and released publicly Tuesday.
Kenneth Nichols, the teen's father, termed the police officers "a little out of control" and said, "There was no doubt in my mind that they weren't going to charge any of them."
He said police knew of his son's mental health problems and that he is exploring options, including asking an outside agency to investigate.
However, police said the officers who had responded to previous incidents were not the ones involved in the shooting and that officers are trained to deal with people who have mental health problems.
An internal affairs investigation is continuing, said Howard police spokeswoman Sherry Llewellyn. She said the officers, who had been placed on routine administrative leave after the shooting, had been returned to their regular jobs after Broccolino's decision.
Kenneth Nichols said he was unaware of the decision until contacted by a Baltimore Sun reporter.
"Had it been determined that a crime had been committed, we would have reached out to him," said Deputy State's Attorney Mary Murphy.
Police said there had been previous incidents at Jeffrey Nichols' home, including one in which the teen asked police to shoot him.
In mid-September, police were called to the family's home in the 6600 block of Grouse Road. They found that Jeffrey Nichols had cut his arms and took him to a hospital.
On Oct. 7, the teen called police to his home and brandished a knife. He told officers to shoot him and said, "just do it" and "make it quick," police said.
Officers responding to a report Nov. 7 that someone had fired shots in the Hanover area saw a man with a pistol walking along railroad tracks. They followed him and repeatedly told him to drop the weapon, police said. When he continued to refuse, officers shot him.
Police investigators later determined that Jeffrey Nichols' weapon was a pellet gun that looked like a semiautomatic pistol.
The state's attorney's office reviewed police reports and conducted its own investigation of the actions of the six officers who fired their weapons and a seventh who tried to disarm Nichols, according to the office.