This image shows the trail of blood that appears to lead to the body found in the San Francisco arena.
The body of a young man was found floating in the water near San Francisco's Fort Mason this morning after a blood trail was reported Monday night, police Lt. Troy Dangerfield said.
Police have not yet released the man's name but said he was white and about 19 years old. They are investigating the death as a homicide.
Police received a call at about 10:30 p.m. Monday from someone who had seen fresh blood in the area of Buchanan Street, Dangerfield said.
Officers responded, found the blood and searched the area but didn't locate any victims.
This morning, at about 6:36 a.m., another caller reported a body floating in the Bay near a pier at Fort Mason, Dangerfield said. Police returned to the area and located the body, which was fully clothed.
Investigators discovered a trail of blood leading from outside a post office at Beach and Buchanan streets to a spot near where the body was found, he said.
"The trail goes all the way across the street toward the pier," Dangerfield said.
Tuesday morning, there were still spatters of blood outside the post office door. The trail led across the Beach Street intersection and into a parking lot where a large bloodstain was visible. Trickles of blood led from there toward the water.
Mid-morning, police expanded the crime scene and had blocked off Buchanan Street between Bay and Beach streets, as well as parts of Marina Boulevard.
Pedestrians and bicyclists, including a steady stream of tourists on bikes rented from Fisherman's Wharf, are being detoured around the crime scene.
A Sausalito man riding his bike through the area this morning was taken aback when he learned what had happened.
"I can't believe it," said the man, who declined to give his name.
Police are speaking with potential witnesses and are trying to piece together what happened.
Anyone with information about the case is asked to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.