Updated 03/07/12 – 9:40 p.m.

CROWN POINT, Ind. (CBS) — Police in northwest Indiana are focusing their search on a dark blue GMC pickup truck or SUV in their investigation into the hit-and-run crash that killed a Lake County Sheriff’s correctional officer and seriously injured three others. Authorities also said the driver apparently accelerated shortly before hitting the officers as they were jogging.

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“One of the officers, when we talked to him at the hospital last night, said that they heard aloud revving of the engine. That’s when they simultaneously were struck. So, obviously, there was no attempt to stop,” Lake County Sheriff John Buncich said Wednesday.

Around 7 p.m. Tuesday, the officers were jogging along a stretch of 93rd Avenue near Main Street in Crown Point, outside of the Lake County Jail, when a dark blue GMC SUV or pickup truck slammed into them and fled the scene. They were jogging as part of a training session — some for the tactical team, others for the special operations response team.

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The collision was so severe, 25-year-old mother and Marine Corps veteran Britney Meux was killed instantly. She had been with the sheriff’s department for three years.

“We lost one of our family last night,” Buncich said.

The three other officers — David Murchek, 26; Latasha Johnson, 34; and Delano Scaife, 22 — were seriously injured in the crash. Scaife was so badly injured, he was airlifted to a hospital in Indianapolis, where he underwent surgery Wednesday morning. Johnson suffered a broken arm and possible internal injuries and remained hospitalized at Franciscan St. Anthony Health in Crown Point in fair condition on Wednesday. Murchek was released from the same hospital on Wednesday.

Authorities and police union officials have put up a combined $11,000 in reward money for information leading to an arrest.

Police said they are confident the vehicle is a GMC pickup truck or SUV, because of a passenger side mirror that was broken off in the crash.

“We’ve narrowed it down a 1999 to 2006 GMC Sierra, or a 2003 to 2006 GMC Yukon,” Buncich said Wednesday. “There should be extensive damage to the passenger front lights, fog light, the hood area, and of course the side mirror on the passenger’s side is missing.”

Police urged the hit-and-run driver to come forward voluntarily.

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“Why would they flee?” the sheriff said.

Surveillance video from the area has provided police with a promising lead.

“We have one vehicle that was seen leaving this area of the parking lot of the complex, coming out without lights on,” Buncich said.

He said police will continue to work around the clock until they find out who killed Meux, and nearly killed three of her colleagues.

“When it’s one of your own … you know, we’re not going to give up on this,” Buncich said.

A vigil was held Wednesday evening outside the Lake County Jail to honor Meux.

For everyone in the local law enforcement family, it was a hard walk along a path – lit by the lights from police squad cars – from the jail to the roadside spot where Meux died.

Her mother tearfully joined the group, standing around a cross with her daughter’s picture.

“I thank God for her. She’s gone; out of sight, but not out of mind,” Jackie Meux said. “Keep me in your prayers and I will keep you guys in our prayers. So, thank you much, thank you much, thank you much.”

Britney Meux’s friend and colleague, deputy warden Niecy Gore won’t forget the moment when she learned of the fatal hit-and-run.

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“I was here in jail on fifth floor; and when I got the call, I actually ran from … all the way from the 5th floor, all the way to 93rd, to where it happened,” Gore said.