Police have been looking at Le's former friend from the beginning. Police detained her the day after Le disappeared, but let her go a short time later. Now police say they have enough evidence to keep Esteban behind bars.
The family of the missing nursing student said on Wednesday that they are devastated by the news that Le's former friend has been arrested on suspicion of murder.
"No words can adequately explain the emotions that we feel right at this moment," cousin Kristine Dinh said.
The 27-year-old Esteban was booked into the Alameda County Jail on one count of murder. Court records reveal Esteban has a history of violence and mental illness.
The single mother of a little girl, Esteban has been considered a person of interest in Le's May 27 disappearance from the beginning.
In a phone call to ABC7 News just days after Le's disappearance, Esteban denied killing Le. In the same phone call, Esteban admitted she hated her former friend because of Le's friendship with Esteban's boyfriend Scott Marasigan.
"We could speculate as to motive," said Lt. Roger Keener with the Hayward Police Department. "I know that there has been information relative to Giselle's relationship to Michelle in the past."
People who know Esteban describe her as someone who is prone to outbursts, including yelling and hitting.
"Well when she gets mad, she really gets mad, but I don't know if she could do this or not," Corazon Marasigan said.
Marasigan's son Scott has a 5-year-old daughter with Esteban. They were all friends with Le, but Esteban had a falling out.
"She's been jealous of Michelle ever since. I guess it's a rivalry or something," Marasigan said.
"Yeah, she was unstable, prone to mood swings, violent," Travis Marasigan, Scott's brother, said.
In the months since Le's disappearance, there have been extensive searches of the East Bay area, with a particular interest on the hills around Sunol.
Le's body, though, has not been found, and even after police classified her disappearance as a homicide, the family held out hope that the 26-year-old might be found alive.
"At this point, she is still missing, and we will fight to bring her home every day until we have her with our family again," Dinh said.
Police say they found a pair of tennis shoes with Le's DNA on the bottom during a raid of Esteban's home during their investigation. Cell phone records also show Le and Esteban's phones traveled in tandem after Le disappeared from the Kaiser hospital where she was a student.
The family is planning another search for Le the weekend after next.
Esteban is scheduled to be in court Thursday afternoon to be formally charged with murder.
ABC7's John Alston contributed to this report.