A former Boston police sergeant who amassed 40 complaints from residents, colleagues, and supervisors over two decades with the department and resigned after agreeing to a suspension is now a state-licensed private investigator.

Martin B. Kraft, a 32-year veteran, resigned from the department in 2015 and received a private investigator’s license last year. He announced his new business, Kraft Investigations Group, on social media in March.

The Massachusetts State Police, which licenses private investigators and vets applicants, “does not review any history of citizen or internal complaints’’ against former police officers who apply for a license, a spokesman said. But defense attorneys who rely on private investigators believe the complaints should be considered.

“You want to make sure an investigator is vetted carefully,’’ said Robert Harnais, an attorney in Quincy who has worked with private investigators.

After the Globe inquired about Kraft’s license, State Police scheduled a hearing on his application for March 3.

Asked whether the record of complaints should prevent him from being a private investigator, Kraft said, “That was some excellent police work. Everybody complains.’’ He declined to comment further.

According to Boston police records, Kraft was the subject of complaints alleging disrespectful treatment, untruthfulness, neglect of duty, unreasonable judgment, and use of force between 1994 to 2014. Fifteen of the complaints were sustained, meaning evidence supported the accusations. Six of those complaints were lodged by supervisors and colleagues.

David Procopio, a State Police spokesman, said the agency “would only investigate employment-related complaints if the applicant [for a private investigator’s license] had a dishonorable discharge or equivalent.’’

A Boston Police spokesman, Lieutenant Detective Michael McCarthy, said Kraft “resigned after signing a settlement agreement’’ in which he accepted a one-year suspension that was “deemed already served.’’

Procopio was unable to say whether any of that information should have disqualified Kraft from receiving an investigator’s license, but said State Police would review his application to determine whether any information should have prompted further checks.

Civil rights attorney Howard Friedman said State Police should always consider certain complaints against former police officers applying to be private investigators, such as those alleging untruthfulness.

“Usually private investigators are talking to people, getting statements, going to the scene and finding new witnesses . . . they are supposed to go out, get the facts, and get the truth,’’ Friedman said. “If a person has problems with truthfulness, that’s concerning.’’

Peter Elikann, a criminal defense attorney, said complaints should not necessarily disqualify an applicant, and decision should be made case-by-case.

“Just because there was some wrongdoing long ago it shouldn’t automatically limit someone as a private investigator,’’ he said.

There are 780 licensed investigators in the state, and most applicants are approved, Procopio said. They must provide three letters of support and undergo criminal history checks. Anyone with a felony conviction is disqualified.

Private investigators do not have the power to arrest and can be armed only if they have a valid license to carry a firearm.

As for former police officers, State Police check to see if those applicants have ever had firearms permits revoked; if so, that would prompt further investigation. Kraft did not have his firearm license revoked, Procopio said.

On his company’s website, Kraft offers services related to background checks, locating lost or stolen property, personal protection, event details, information gathering for criminal and civil cases, and research related to infidelity, domestic violence, custody battles, and missing persons.

He is on the Licensed Private Detectives Association of Massachusetts board, according to the association’s website.

A Vietnam veteran, Kraft was fired by then-Commissioner Francis M. Roache, who was his father-in-law, in 1988 for failing to disclose that he had received psychological treatment prior to his employment.

Two years later, a Superior Court judge ordered that Kraft be reinstated, ruling that state law prohibits the department from asking about admissions to mental health facilities.

In 2005, he was disciplined for double-dipping on private detail shifts.

Jan Ransom can be reached at jan.ransom@globe.com. Follow her on Twitter at @Jan_Ransom.