Homicide investigators are hunting for clues after an unidentified man and woman were mysteriously left bound and gagged on a San Francisco street Sunday night.

About 8:30 p.m. Sunday, police said, a man in his 20s and a teenager were found tied up but still alive in the 900 block of Brussels Street near Mansell Street, which is located on the northern end of Visitacion Valley, blocks away from Phillip & Sala Burton Academic High School.

They were taken to San Francisco General Hospital, where the man died about midnight. The female victim remained at the hospital Monday with life-threatening injuries, police spokesman Officer Albie Esparza said.

Police revealed little about their investigation. No suspects had been identified as of Monday, Esparza said, adding that officers are reaching out to the public in hopes of getting help to piece together the brutal homicide.

Stunned neighbors who came upon the grisly scene said Monday that they did not know the victims.

One neighbor, who wished to remain anonymous for fear of retaliation, said she believes the victims were intentionally left there.

“It’s obvious this was a message,” she said. “This was planned.”

Another neighbor, who also wished to not be identified, said he saw nothing unusual on the block when he went to the grocery store about an hour before the incident. After learning about what had happened, he said his 7-year-old son asked him, “That means a murderer drove by our house?”

Splotches of dried blood remained on the concrete Monday. Some were mixed with skid marks from a vehicle, although it’s unclear whether those marks were related to the incident.

Other neighbors said nothing like this has ever happened in their relatively quiet community.

maldax@sfexaminer.com