Rio Claro, Costa Rica ? The mother of a slain Kansas University student who traveled to Costa Rica for the trial of the three people accused of killing her daughter has received death threats, police said Tuesday night.

Authorities responded to the threats by assigning police officers to protect Jeanette Stauffer, who is staying with other family members in the southern community of Golfito, where the trial is taking place, said Luis Angel Nunez, chief of police for a region that includes Golfito and neighboring Rio Claro.

The trial began last week and was scheduled to resume today, after a four-day break. Nunez said there would be twice as many police officers attending the trial this week as there were when it began and added that authorities intended to limit the number of observers allowed inside the courtroom to better protect Stauffer.

Nunez said a caller threatened to kill Stauffer, but would not say if the threat was heard by Stauffer directly or if it came into the courthouse office of the prosecutor in Golfito.

He also declined to confirm when the call was received.

Shannon Martin, a 23-year-old KU student from Topeka, was stabbed to death on May 13, 2001, after she left a nightclub in Golfito, about 100 miles south of the Costa Rican capital, San Jose. Martin was in this country to gather specimens for a biology project.

On Friday, a key witness in the case, Rosibel Munoz, was forced to give her testimony behind closed doors because of death threats. Shortly before Munoz was scheduled to testify, the courthouse office of the prosecutor received a call saying, “If Rosibel testifies, we’ll kill her.”

Stauffer, who had offered up to $50,000 to anyone who could provide information about the killing, has traveled to Costa Rica repeatedly since her daughter’s death and has vowed to remain in Golfito for the duration of the trial. She was unavailable for comment late Tuesday night.

Rafael Zumbado Quesada, 52, Kattia Cruz, 29, and Luis Alberto Castro Carillo, 33, have been accused of homicide in Martin’s killing.

Stabbed 15 times, Martin’s body was found along an airport access road about 100 feet from the home of the Costa Rican family she was living with.