Des Moines police are crediting some good police work and luck with allowing them to quickly make an arrest in a murder case. 26-year old John Graves is charged with first-degree murder in the death of 50-year old Darlene Avant. Police Sergeant Bruce Elrod says Avant was spotted by two police officers in a convenience store early Wednesday morning accompanied by a man. Elrod says the officers recognized Avant as a known prostitute and took down the license plate number of their car. The license plate number led to Graves.Elrod says Avant has a long record of prostitution and drugs arrests. He doesn’t know if Graves was a customer of Avant’s.Elrod says they’re still trying to determine a motive for the killing.Avant’s body was dumped in a remote area on the south side of Des Moines, and Elrod says it appears she was stabbed to death.Avant’s death was the second homicide in Des Moines Wednesday. Police say 31-year old Tung Thahn Le was shot to death on the south side of Des Moines in what’s believed to be a drug dispute. 30-year old Rodney Wessel Junior was taken from the scene with a gunshot wound to the stomach. Wessel was listed in fair condition and police are searching for his cousin, who they believed witnessed the incident.