INDORE, India—When stock analyst Nitin Mangal co-wrote a research report in August 2012 telling investors to sell shares in companies that were part of the Indiabulls Group, a big Indian real-estate and financial conglomerate, he figured the company wouldn’t like it.

He didn’t expect what happened.

More than two years after his report appeared, police arrested Mr. Mangal last November and took him on a five-day trip to two Indian cities, accompanied by an Indiabulls lawyer. The purpose of the trip, police say, was to gather evidence related to alleged defamation and other accusations tied to his research report.

Mr. Mangal says the trip was intended to intimidate him. One night, he said, he was chained to his bed. He also said he was threatened by the lawyer with physical harm if he didn’t cooperate with Indiabulls.

“I feared for my life. I didn’t know what they would do to me,” said Mr. Mangal, who eventually was brought to Gurgaon, a suburb of the Indian capital of New Delhi, where he was then jailed for 12 days, before being released on bail. He hasn’t been charged with committing a crime, though police have sought approval from a judge to file charges, and a hearing is to take place in October.