Two sheriff's deputies were shot dead and two wounded in LaPlace, Louisiana on Thursday by an attacker armed with an assault weapon, police said.
The gunman shot one St. John Parish deputy while he was directing traffic in an off-site parking lot for the Valero Energy Corp's St. Charles refinery, Sheriff Mike Tregre said.
The gunman fled the scene, and officers investigating the incident ended up at a trailer at a trailer court. While they interviewed two suspects, a person came out of the trailer with an assault weapon and fatally "ambushed" two officers, he said.
"At this point, it's a very hot investigation and it's ongoing," Tregre said at a televised news briefing.
Five people are believed to be in custody. Some suspects were shot and wounded, he said.
Details were still sketchy, but Tregre said: "There are no other perpetrators on the loose."
The slain deputies were identified as Brandon Nielsen, 34, and Jeremy Triche, 28. The wounded deputies were identified as Scott Boyington and Jason Triche.
The Louisiana State Police have taken over the investigation and are looking into what led to the initial shooting. A State Police spokeswoman told CNN that two of the officers were off-duty and two were on duty.
LaPlace is about 25 miles west of New Orleans. Valero said in a statement that refinery operations were not affected.