The gunman who opened fire at Johns Hopkins medical complex in Baltimore today, critically wounding a physician, killed his mother and then himself during a standoff with police, reports MSNBC.

The suspect, described as an African-American male in his 30s, barricaded himself in a room of the hospital's thoracic center on the eighth floor of the hospital's Nelson Building, reports the Baltimore Sun. The shooter was reportedly upset about his mother's treatment at the hospital and shot the doctor in the stomach during surgery, according to a CNN report.

Sections of the building were placed on lockdown around 11:15 a.m., while other areas were evacuated. Baltimore PD officers and Baltimore County PD's SWAT unit including snipers, arrived at the scene. The agency provided updates of the incident via its Twitter page, such as "Suspect may have been using an alias. Police are working to confirm identity."

The lockdown has been lifted; however, visitors are asked to stay away from the Nelson Building, according to the hospital's website. Johns Hopkins employees with identification are asked not to attempt access to the eighth floor of the building.

Additionally, information on the wounded doctor, who is being treated at the facility, has not been released due to privacy and confidentiality policies.

Read a full CNN report.