Each of the applicants was given a list of questions as part of the interview process and was scored, city officials said.
It is the mayor's choice to decide who holds the police chief's job, and Smith decided to hire Subelsky last month, city officials said.
Subelsky, 59, of Hedgesville, W.Va., was sworn in before a crowd that included his wife and son. There was a round of applause from the crowd and Charles Town City Council members following the swearing-in.
"I appreciate the trust you have put in me. I look forward to the challenges of it," Subelsky said.
Thirty minutes were set aside before the beginning of the meeting to give Subelsky a chance to meet with local residents and reporters.
Subelsky said his first day of work at the police department was Tuesday. The Detroit native said he has not had a formal meeting with the department, but will do that today.
Subelsky repeated his earlier comments that the city needs to work as a team to address crime issues. He said he wants to keep in contact with city residents about law enforcement issues and that it is important that citizens contact the police department about problems they see.
"And the folks here are part of that team," said Subelsky, gesturing toward the table where city council members sit.
Smith formed a police task force to search for a new police chief and one of the members of the committee was Jefferson County Sheriff Everett "Ed" Boober.
Boober, who was at Tuesday's meeting, said Subelsky has expertise that will "take the city of Charles Town forward for many years."
Subelsky joins the police department at a time when the county is facing crime problems such as gangs, and he has emphasized the importance of local law enforcement agencies working in partnership to deal with them, Boober said.
"He has a very solid approach, a very solid plan," Boober said.
Subelsky declined to talk about specifics about how he plans to run police work in the city. He has said in the past that he first wants to discuss those issues with members of the department before making any comment.
"Come back in 30 days and I'll answer your question," Subelsky said.
Subelsky began his government career as a U.S. Army infantry officer and was a rifle platoon leader in the Vietnam War.
He spent two years as a police officer in Houston and later worked as a special agent investigator in the Houston, Cincinnati and Washington divisions of the FBI.
At the Washington FBI field office, Subelsky worked on domestic and overseas terrorist programs and was the SWAT team leader for the office for 10 years.
In 1998, he was promoted to the position of special-events management unit chief at the FBI's national headquarters, which involved implementing counterterrorism response programs for special events like Olympic Games in the United States.
In 2001, Subelsky retired from the FBI and started working for the U.S. Department of Energy, initially assigned as a counterterrorism plans officer.