Students from Celia Cruz Bronx High School of Music, from which William Rodriguez retired as principal in March amid investigations, performed at Grand Central Terminal.

The city has taken its final step in disciplining a Bronx principal who colleagues and investigators said had played fast and loose with school funds.

William Rodriguez retired from the Celia Cruz Bronx High School of Music on March 8, the same day he told people at the school that he would be stepping down. After a two-year-old inquiry, investigators found that he had billed the city for time he did not work and had a school employee assist him on personal projects.

A spokeswoman told GothamSchools in March that the Department of Education would bar Rodriguez from working in city schools again. She also said the department would deduct the amount that Rodriguez had been overpaid from his final paycheck and benefit payout.

Now, the city’s Conflicts of Interest Board has fined Rodriguez $2,500 for paying an employee to work on his music business using school resources.

According to the ethics board’s report, which Rodriguez signed and certified, Rodriguez paid Michael Greene, a paraprofessional at the school, “at least $1,888.15” over three years to produce two albums, create a website, and register Rodriguez’s company, NYRR Music, Inc. Rodriguez and Greene conducted their exchanges during school hours and using their Department of Education email accounts, according to the report.

The payments violated the city’s prohibitions on employees entering into financial relationships with subordinates; having business interests that compete with their official duties; conducting personal business during work hours; and applying city resources for personal uses, according to the disposition, released today.

Rodriguez, who had worked in city schools since 1982 and founded Celia Cruz in 2003, earned $150,926 a year at retirement, according to the city.

An assistant principal, Jerrod Mabry, took over as interim acting principal in March. Educators say he has begun to address some of Rodriguez’s leadership problems that were not grounds for investigation, including that he favored the school’s music offerings at the expense of its academic program.

“It is my hope that we will work together to continue to provide the students of Celia Cruz the best possible opportunities in preparing them to be outstanding musicians and academic students,” Mabry wrote on the school’s website. “My door is always open and I welcome your input. Please feel free to stop in or call to make an appointment to discuss any concerns, suggestions, or ideas to help make this the best year yet!”