Longmont police have arrested three people in connection with the Tuesday stabbing death of a 19-year-old man.Lakesha Marie Crutcher, 20, Mariena Amber Harris, 19, were arrested on suspicion of second-degree murder early Wednesday morning. Robert Glenn Wittmer, 35, was arrested on suspicion of being an accessory to murder.Police had been looking for two men and two women who were observed leaving the area where Logan Cameron Steele Sisson was attacked. They were in a black and red 1997 Geo Tracker, according to police. Wittmer owns a car matching that description.Longmont police said they discovered that Harris and Crutcher were involved in a physical fight with Sisson in a nearby park. They said the three moved toward Wittmer's vehicle where Sisson was stabbed.Police said the investigation revealed that the suspects had all attended a "420" party in the 1900 block of Meadow Drive prior to the incident.Sisson knocked on a nearby home for help and was rushed to a local hospital, where he died of his wounds.