Updated 09/07/11 – 9:05 p.m.

CHICAGO (CBS) — The family of a Chicago woman who was struck and killed on the Eisenhower Expressway last week has filed a lawsuit against Illinois State Police, who dropped the woman off at a gas station a couple hours after she was arrested for drunk driving.

Diana Paz was arrested early last Friday after driving the wrong way on the Eisenhower and failing field sobriety tests. She bonded out a couple hours later and, after telling police she had no family or means of getting home, she asked for a ride to a nearby gas station.

About half an hour later, authorities were notified that she had been struck by a vehicle on the Eisenhower.

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As CBS 2’s Suzanne Le Mignot reports, her family said police never shouldn’t have released her in her condition and now they want answers.

“We really don’t know what really happened, or how it happened,” said Maria Paz, Diana’s sister, after the family filed the lawsuit on Wednesday. “It seems like it is not fair for her, for our family, for her, for this … for her to end like this.”

Diana Paz’s life ended on the Eisenhower Expressway last Friday. Hours earlier, she was pulled over at 3:23 a.m. on Sept. 2 for driving in the wrong direction on I-290. She refused a breathalyzer and failed a field sobriety test.

People who celebrated Diana’s birthday with her earlier that night told her family that Diana had been drinking heavily that night.

Paz was taken into custody and brought to the Westchester Police Department. She bonded out at 5:40 a.m. the same day.

An Illinois State Police spokesperson said Paz signed herself out with an I-bond. She asked police to take her to a nearby BP gas station. Moments later, the 25-year-old mother was walking in a marked median area on the Eisenhower Expressway. That’s when she was hit by a truck driver and killed.

“She was my other half. She was my best friend,” Maria Paz said. “We just want the answers that we’re looking for. Why did this happen? Why did they let this happen? We just want justice.”

“They should have kept her until she was sober, not until … just because she requested to be dropped off at a gas station,” she added.

Illinois State Police said Diana Paz was alert and coherent at the time of her release. State police are not required to transport motorists, but as a courtesy, officers will transport stranded motorists within a reasonable distance. There’s no policy requiring Illinois state police to do this.

“We’ll see what the protocol is for the state police in dropping off young girls after they’ve been arrested for DUI,” said Paz family attorney Tim Cavanagh. “My guess is that they violated their protocol and that they’re going to be held accountable for that.”

Cavanagh filed a motion on Wednesday for all evidence in the case to be preserved – meaning all medical records and video at the BP gas station where Paz was dropped off.

Cavanagh said he believes the video will show that Paz was intoxicated when she left the gas station.

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