WALNUT CREEK -- After multiple surgeries and days of rehabilitation, a 23-year-old woman was released from John Muir Medical Center on Wednesday, more than a month after a pickup driver veered onto the sidewalk, striking her and killing her mother-in-law.

Sheng Hahn was put in the hospital's intensive care unit following the Sept. 8 crash; she suffered two torn ligaments in her right knee and head injuries severe enough that family and friends feared she may have brain damage.

But on Wednesday, she returned to the Walnut Creek residence she shares with her husband, Casey. Sheng's mother and grandmother from China are staying there, too, to help her start her outpatient recovery.

"There's still a pretty long road," Casey Hahn said Thursday. "But we'll be together, her family and me. She's happy to be home."

On Sept. 8, the driver of a Chevrolet pickup veered onto the sidewalk on North Main Street just south of the Interstate 680 overcrossing. The driver struck Sheng Hahn and her mother-in-law, 52-year-old Sherry Hicks, who was killed. Casey Hahn and another man were not injured.

The driver, 54-year-old Hossein Tabrizi, of Walnut Creek, was arrested on suspicion of vehicular manslaughter. He was released from jail after police did not submit charges to prosecutors within the 72 hours required by law.

Walnut Creek police Capt. Tim Schultz said Wednesday that investigators are awaiting results from a toxicology report.

Criminal law expert Dean Johnson, of Redwood City, said fatal car crash investigations can take time, and that prosecutors want to have "all their ducks in a row" before moving forward.

"You want to look at all kinds of things that the driver might have been doing," he said. "If they were speeding, reckless driving, if the driver was under the influence of drugs or alcohol. ... If all that turns out negative, you may say this is at best a civil case. If some of that shows the driver was in some way criminally negligent, then you are going to file a case. It's often a long, hard road to go down."

Casey Hahn has been overwhelmed by the support he and his wife have received in their new town. The couple moved to Walnut Creek this past summer after graduating from UC Santa Barbara and getting married.

"I just thank everybody that has given me thoughts and prayers over this period," he said. "It's really nice to know you have support in a new city."

Contact David DeBolt at 943-8048. Follow him at Twitter.com/daviddebolt.