That second victim was believed to have been sharing a home with Kevin Daigle, 54, who authorities say has been charged in Vincent's death.
The 44-year-old veteran trooper was shot Sunday during the course of a traffic encounter with Daigle, whose pickup was stuck in a ditch by the time Vincent arrived, according to Col. Michael Edmonson, the police force's superintendent. Several people had called to report the suspect had been swerving all over the road. Vincent died of his injuries Monday.
"As an organization, we are heartbroken over this senseless and tragic death," Edmonson said. "Our thoughts and prayers are with his surviving wife, Katherine, and his son (9-year-old) Ethan as well as his entire extended family," including two brothers who are also in law enforcement: Terrell Vincent, who's also a trooper, and Keith Vincent, who's chief of police in Iowa, Louisiana.
Vincent realized the suspect's vehicle matched the description of a truck whose driver had reportedly been driving recklessly. He started talking to Daigle, who appeared to be impaired and was alone in the truck, Edmonson said.
According to police, Daigle opened the truck's door and came out with the shotgun.
"You could hear him breathing, telling him, 'You're lucky. You're lucky. You're going to die soon.' That's the words that came out of his mouth," said Edmonson, who said he listened to a recording of the interaction.
The suspect tried to flee the scene, but other motorists wrestled a shotgun from him and detained him with the trooper's handcuffs, Edmonson said.
"Thank God for those good Samaritans," he told CNN's Don Lemon. "They are heroes."
Edmonson said a man got Daigle to the ground and later got on the police radio to ask for help.
"Total disregard for his own safety. He did what very few people would do," he said.
Daigle is being held at the Calcasieu Parish Jail.
'This didn't make any sense'
Investigators interviewing Daigle learned about an altercation at a home in Moss Bluff, just north of Interstate 10 in southwestern Louisiana, where deputies were already headed to do a welfare check after a man did not show up for work Monday, Calcasieu Parish Sheriff Tony Mancuso told reporters.
When they arrived, they forced their way inside and found the second victim. Authorities are not yet identifying him because his family has not been notified.
"We do believe foul play is involved, and we are investigating it as a homicide," Mancuso said.
In discussing a possible connection between the two slayings, the sheriff said that investigators are looking into the exact relationship between the second victim and Daigle.
"We do have information to believe that he (Daigle) was a resident at that location, maybe not permanently, but at least staying with him (the second victim)," the sheriff said.
He stressed that authorities were just starting to process the scene and do not have a lot of answers. But he hoped they would have more soon.
Mancuso said he hadn't understood why the situation between Daigle and the trooper escalated like it did.
"This didn't make any sense. This may make a little more sense to us now, as this unfolds," he said.
'An honorable husband, father'
Vincent is the first trooper to be killed in a hostile encounter since Trooper Donald Cleveland was murdered near Lafayette in 1977, police said.
Vincent had a lifelong dream of becoming a trooper and joined the Louisiana State Police in 2003. Previously, he was with the Lake Charles Police Department for a decade.
"During his 12 years of service, he received 13 awards and commendations, including the department's Professional Excellence and Meritorious Service Awards as well as numerous Unit Citations for his dedicated and selfless duty throughout the state. He had also served in the United States Army during Operation Desert Shield and Operation Desert Storm," a state police statement from Sgt. Nick Manale said.
Vincent will receive the full honors associated with a death in the line of duty, Manale said.
"Trooper Vincent epitomizes all that is great about our organization. He didn't just believe in our core values, he lived them. The citizens of this state were well served by Vincent, and I know they join us in our collective grief," Edmonson said.
Louisiana Gov. Bobby Jindal ordered flags at state buildings to be flown at half-staff until Friday.
"Steven was an honorable husband, father and state trooper who courageously served our state for over a decade," the governor said in a statement. "Brave men and women like Steven put their lives in danger every day to protect our families, and we are extremely grateful to them for keeping us safe."