Miot Patrice Jacquet, a U.S. Navy veteran, did not think twice about helping an American military contractor with a dangerous mission in his native Haiti.

The company, Studebaker Defense, had an impressive pedigree: Its board is run by Wesley K. Clark, a retired American general and a former NATO supreme allied commander.

But instead of helping wrest Haiti back from gangs, the operation collapsed. The American team was forced to leave early, a cache of AR-15-style rifles was stolen and seven months ago, two people working with the team — including Mr. Jacquet — were abducted, remain missing and are most likely dead.

Suspicion has focused on corrupt police officers, according to two high-ranking Haitian police officials.

With Haiti engulfed in gang-fueled violence and other nations largely unwilling to send significant military aid, the government says it has no choice but to turn to private defense contractors, including the Blackwater founder Erik Prince, to regain control of the country.

But the aborted Studebaker mission — and the abductions and possible killings of a police officer, Steeve Duroseau, and his Haitian American cousin, Mr. Jacquet, an assistant hotel manager in Haiti who worked with Studebaker — underscores the complicated risks of private military contract work in a country where graft, killings and kidnappings are rampant.