Mr. Fustolo said the move was counterproductive because there was no way for him to find a solution to pay his creditors back. But he refused to give up his fight and filed whistle-blower claims purporting to show tax fraud at Old Hill, documents show. The Securities and Exchange Commission and the Internal Revenue Service declined to pursue his claims.

Mr. Fustolo used those filings as the basis for posts, on a website called Whistleblowers International, that claimed Mr. Howe was being investigated for fraud related to the tax treatment of loans in the portfolio, according to the Massachusetts attorney general, Maura Healey, who charged Mr. Fustolo in 2015 under a new online-harassment statute .

“I wanted to get on the record that I believed the bankruptcy was frivolous,” Mr. Fustolo said. “I didn’t really have a hope at that time. I wanted to notify them. I wanted to call them out.”

Mr. Howe said he had brushed off the posts at first. But when he saw how they were affecting his business, he hired a cybersecurity firm to determine what had happened.

The firm traced the posts to a Florida blogger, Dylan Potter, who admitted to investigators that Mr. Fustolo had paid him to create Whistleblowers International. With Mr. Potter’s cooperation, the authorities issued an arrest warrant in Massachusetts for Mr. Fustolo.

Mr. Potter said in the arrest warrant that Mr. Fustolo had asked him over email in 2014 to conduct a “negative internet P.R.” campaign and directed him to use search strategies that would produce the articles when people searched for Mr. Howe’s name. He also paid Mr. Potter to use online services to send out releases containing the false information.

Around the same time, the arrest warrant said, Mr. Fustolo contacted someone who specialized in ranking negative articles high in searches, asking for assurances that the campaign would keep the negative articles visible.