Topeka The reward has grown to nearly $50,000 for information leading to a conviction in the stabbing death of a Kansas University student killed while studying in Costa Rica.
Shannon Martin, 23, was killed last May while finishing a research project on the Central American country's ferns.
No one has been charged with killing, although Costa Rican authorities since November have been holding Katia Vanesa Cruz Murillo, 27.
Investigators do not think Cruz acted alone and are looking into the possibility that at least two men were involved, Jorge Rojas, director of Costa Rica's Judicial Investigative Police, told the Tico Times, an English-language newspaper in Costa Rica.
Cruz has offered little information. Officials told Martin's mother, Jeanette Stauffer, it probably would take a substantial reward to persuade any witness to come forward.
Stauffer said the nearly $50,000 in pledges most of them oral have come from corporations.
She plans to go to Costa Rica to spread the word about the reward.