The force said in a statement on Friday: “The body was found at around 10:30am today by officers who were carrying out searches as part of the investigation into the death of a teenager who was shot at an address in Lighthorne Avenue, Ladywood, last Sunday.
“The body found today, on land next to a canal on Lighthorne Avenue, is believed to be that of a 17-year-old boy. The discovery is being linked to the murder of the 16-year-old.
“At this time we are not looking for anyone else as part of our investigation into the death of the 17-year-old.
“A gun was found at the same time and in the same area as the body found today and will be forensically examined.”
A third person, a 17-year-old boy, was arrested as part of the initial murder investigation earlier this week.
He remains on bail while police establish the circumstances of the first death, and he has not been arrested in connection with the second death.
Police launched a murder investigation on Wednesday after the first body of a 16-year-old boy was found with gunshot wounds at an address in the inner-city suburb of Ladywood in the early hours of Sunday.
He was rushed to hospital in a critical condition and West Midlands Police revealed he died on Tuesday as a result of his injuries.
Police said on Tuesday that detectives were trawling CCTV, with neighbourhood officers in the area to offer reassurance and act as a point of contact for anybody with concerns.
West Midlands Ambulance Service said they were called at 12:26pm on Sunday, and sent two ambulances, two paramedic officers, a trauma doctor and critical care paramedic to the property on Lighthorne Avenue.
A spokesperson spokesperson said: “On arrival, crews found the patient in a critical condition. Ambulance staff immediately began administering advanced life support.
“He was conveyed to hospital on blue lights in a life-threatening condition with the MERIT trauma doctor travelling on board to provide continued treatment en route.”
Since discovering the second body, Detective Superintendent Shaun Edwards said on Friday: “This is a tragic development in our investigation and our thoughts are with everyone who has been impacted by the events of the last week.
“Our investigation into what has happened will continue for some time, and we will be supporting the families involved throughout.
“Neighbourhood officers continue to patrol the area to offer reassurance, and I’d encourage anyone with information to get in touch with us.”