Lopez, 25, pleaded not guilty to first-degree murder Thursday in the killing of 22-year-old Brittany Dawn Killgore.
Bail was set at $3 million at her arraignment in Vista Superior Court, north of San Diego. She could get life in prison if convicted.
Prosecutor Patrick Espinoza said Lopez was found with the suicide note in a Ramada Inn near the airport in San Diego on Tuesday, but no further details were released about the note.
Another Marine, Louis Ray Perez, 45, remained a person of interest in the case. Investigators say he was the last person seen with Killgore.
San Diego County District Attorney Bonnie Dumanis declined to discuss evidence or say if there were additional suspects.
"I understand there's a great deal of interest in the crime and many unanswered questions," she said. "Answers will come in time as this case makes its way through the criminal justice system."
Killgore was last seen on April 13, four days after she filed for divorce from her husband, Lance Cpl. Cory Killgore, who was deployed to Afghanistan seven months ago.
Neighbor Patricia Pagdilao said Brittany Killgore often went out with friends after her husband shipped out overseas.
"The only time I ever saw her was with friends, either on the way out or on the way home," Pagdilao, 20, said.
After she disappeared, Killgore's cellphone was found in the Gaslamp District, an area of bars and restaurants in downtown San Diego.
The couple from Missouri was married in July 2010. Brittany Killgore cited "irreconcilable differences" in her divorce filing, which gave no other details.
Cory Killgore has not been named as a suspect or person of interest and is returning to California after learning about the case.
Lopez's attorney Dean Broyles said he didn't know if his client knew Perez or Killgore, who was reported missing Saturday - one day after Lopez turned 25.
"There's a lot of speculation, a lot of innuendo, a lot of weak allegations and charges out there," he said. "I would caution everyone to not jump to conclusions and prejudge based on all the information flying around right now."
Broyles said Lopez would ask the judge for a public defender after her family sought his help in fielding media questions. Lopez's parents, who live in nearby Escondido, released a statement saying they loved their daughter.
"We pray for the family of Brittany Killgore and ask that the Lord comfort them during their time of grief and anguish," the parents said. "We ask that you pray for all of those impacted by this tragic situation, including our family."
Brittany's father, Darryl J. Wrest of Rolla, Mo., told reporters the family was devastated and wanted to grieve privately.
"Brittany was a beautiful, kind, caring young woman trying to find her way in this world. Family and friends love and miss Brittany beyond words," he said in a quivering voice.
Wrest declined to take questions after reading his statement at San Diego County Sheriff's Department headquarters.
Perez was being held on $500,000 bail after pleading not guilty Wednesday to stealing an assault weapon. Authorities say he took the weapon from a man in early February.
It was unclear if the weapon might have been connected to the killing of Killgore.
Perez has been in the military for 16 years, has no criminal history and is married, said Jeffrey Reichert, his attorney.
Brittany's body was found near Lake Skinner in Riverside County about 25 miles northeast of her modest apartment complex in Fallbrook, a town of 38,000 people known for its avocado orchards, rolling hills and proximity to Camp Pendleton.
Associated Press
