A former high school friend of a missing Northern California nursing student has been arrested on suspicion of murder, more than three months after the victim vanished from a San Francisco-area hospital where she was working.

Hayward police arrested Giselle Diwag Esteban in the death of 26-year-old Michelle Le, who told colleagues she was going to her car during her shift in late May and never returned.

Lt. Roger Keener said Wednesday that police believe an assault occurred at the hospital's parking garage as video surveillance footage shows Esteban at the scene before and after Le's disappearance. Police said they found traces of Le's blood inside her SUV, as well as on one of Esteban's shoes during a search warrant of Esteban's residence.

Le's body has not been found, but Kenner said he hoped Esteban would help police make a discovery.

"The reality is, we don't have Michelle. That's a piece we are not going to close out on until we find her, until her location is known," said Keener at a news conference announcing the arrest. "The facts are some of those questions, such as how Michelle met her demise, may not be answered until Michelle is located."

Esteban was named as a person of interest in June as investigators questioned and searched her Union City apartment. She and Le had been friends at a San Diego high school.

Esteban told KGO-TV at the time that she hated Le because she was friends with the father of Esteban's young daughter. But Esteban said she had nothing to do with Le's disappearance.

Court records show that Esteban's ex-boyfriend, who had custody of their daughter, was granted a restraining order against her three days before Le's May 27 disappearance, according to KGO.

On Wednesday, Keener said he could not speculate a possible motive, including a possible love triangle.

"I don't know the answer to that question and I'm sure our investigators don't know the answer," Keener said. "That answer, I'm assuming, may only be answered by Esteban herself."

Esteban is scheduled for arraignment in Alameda County Superior Court on Thursday.

Authorities classified Le's disappearance as a homicide this summer based on forensic evidence from Le's vehicle, surveillance footage outside the hospital, cell phone records and evidence collected during search warrants.

Keener said that with such a complex investigation that included air and ground searches involving as many as 65 people who did not find a body, police took significantly more time to make an arrest.

"We did not want to rush to judgment. We did not want to fail to turn over every possible piece of evidence," Keener said. "The reality is there isn't one piece of evidence or statement that was necessarily a tipping point. It is the totality of the circumstances as the investigation culminated."

But Le's family members have held out hope, offering a $100,000 reward for her return or for information on her whereabouts and conducting seven searches for her so far.

At Wednesday's news conference, Le's brother, Michael Le and cousin Krystine Dinh, both trembling, said that Esteban's arrest hopefully brings them one step closer to finding Le.

Michael Le, who turns 24 on Thursday, said his sister would always call to say happy birthday.

"I just want to hear her voice so badly and the only thing I'm going to be wishing for is for her to come back home," Le said. "We're still going to do everything we can to bring her back home."

Keener agreed.

"Make no mistake, today's arrest does not mark the end of our investigation," Keener said. "We will not consider this investigation to be complete until Michelle is found."