A trail of blood might have helped the San Francisco Police Department make an arrest in an armed robbery in the Mission District this morning. But in an unusual twist, the blood didn't belong to the robbery victim — the wounded party is one of the suspects, who appears to have shot himself.

According to KRON4, at around 3:30 this morning two armed suspects robbed a man near 23rd and Bartlett Streets.

The men took his wallet and cell phone, then fled on foot, CBS5 reports.

Officers who were patrolling in the area say they discovered a trail of blood down Bartlett Street. They followed it and found the two suspects, both of whom were arrested on the spot.

One of the men was suffering from a gunshot wound to the leg, likely the cause of the blood trail. As the robbery victim was unarmed, police say they believe the man might have shot himself as he ran.

Police also say that they discovered a MAC-10 automatic machine pistol nearby, which they believe was tossed by the suspects as they fled.

The robbery victim was not injured in the incident, police say. The wounded suspect was transported to San Francisco General Hospital and is expected to survive.