A convicted killer suspected of masterminding a bar shooting that left eight people dead in Puerto Rico was arrested aboard a 30-foot boat just after it entered a marina in the U.S. Virgin Islands, federal officials said Wednesday.

Alexis Candelario was detained late Tuesday when Immigration and Customs Enforcement officers at Crown Bay Marina asked for documents during a routine inspection and recognized him, spokesman Ivan Ortiz said.

Candelario initially handed over a fake driver's license, but did not resist arrest when he was identified, Ortiz said.

"Our biggest fear was that another massacre would occur in retaliation," said local prosecutor Ivelisse Dominguez, expressing concern that Candelario might have been targeted. "We were very frustrated because we received no cooperation from citizens."

Four other people aboard the boat were not arrested, Ortiz said.

Candelario was arrested on federal firearm violation charges and could face life in prison if found guilty. He appeared Wednesday morning in a St. Thomas court but did not enter a plea, according to a clerk who declined to be named because she was not authorized to comment on the case. It is unclear if he had an attorney.

Candelario was sent back to Puerto Rico Wednesday afternoon, Ortiz said.

Candelario is one of several suspects in the drug-related shooting at the neighborhood bar on Oct. 17 that injured 20 people, including a 9-year-old girl. A pregnant woman also lost her 8-month-old fetus.

Authorities who suspect he directed the killings are investigating whether he also took part in them, Ortiz said.

Candelario was previously charged in 1991 with attempted murder and was convicted of second-degree murder after an unrelated killing in 2003.

Puerto Rico's justice secretary recently excused himself from the investigation because he had been Candelario's attorney in an earlier case.

The owner of the La Tombola bar and grocery where the shooting occurred also was arrested in late October on federal drug trafficking charges. Two other men linked to the shooting also have been arrested on weapon charges and officials expect more arrests.