She drove 90 miles north to Santa Rosa, parked at a junior college and got into the trunk of her own car — all in order to take her own life. At least that’s the story authorities are giving for the death of electrical engineering doctoral student Mengyao “May” Zhou, 23.

The Sonoma County Coroner’s Office performed an autopsy Friday, finding “no outward signs of trauma to the body.” The autopsy was also unsuccessful in determining a preliminary cause of death.

Officials say it will take several weeks, possibly even a month, before other, more conclusive lab tests can be completed. One of the planned tests is a toxicology screening, which will determine whether any foreign substances were present in Zhou’s body at the time of her death.

Until new evidence comes to light, authorities appear to be sticking to their suicide theory.

“No new information has been developed that would lead investigators to believe foul play is involved,” the Santa Rosa police department said in a press release Friday. Santa Rosa authorities, the lead investigators on the case, added that they are still interviewing people who might have more information.

Investigators, however, continue to leave many pressing questions unanswered.

While police have said that items found in the trunk “indicate the subject may have committed suicide,” they have so far refused to provide further details regarding that evidence. Nor have they offered any explanation for why Zhou’s car was found an hour and a half north of campus or why Zhou would drive to Santa Rosa Junior College in the first place.

Details about Zhou’s car render the case even more perplexing. Police found Zhou’s body in the trunk of her 2006 Toyota Corolla. But according to Toyota, all 2006 Corollas are equipped with a glow-in-the-dark “Internal Trunk Safety Handle,” which allow the trunk to be opened from the inside in the case of emergencies.

Four days after the discovery of Zhou’s body, it is also unclear how much Santa Rosa and Stanford law enforcement are cooperating on the case.

“All we did was take the missing person’s report,” said Marissa, a Stanford Police dispatcher who refused to give her last name.

Other officials at Santa Rosa and Stanford could not be reached for comment over the weekend.

Meanwhile, Zhou’s father, who said that he found out about the discovery of his daughter’s car from a reporter and not from law enforcement, has questioned the suicide theory. His daughter, he says, was planning to edit her resume with him over the weekend she went missing.

“If you’re thinking about your resume, why would you be thinking about suicide?” Yitong Zhou asked in an interview with the San Jose Mercury News. “I don’t believe it. I don’t believe it.”

Zhou also said that his daughter conducted some “unusual” banking transactions before her disappearance, but he did not elaborate on the details.

Zhou was a second-year doctoral candidate in electrical engineering. She was reported missing last Sunday by her roommate, and her body was discovered Thursday in Santa Rosa. Friends who knew Zhou described her as a “driven” and hardworking student and expressed shock upon hearing the news of her death.