A chaotic house party that ended in gunfire and a robbery by a bicycle-riding shooter left two people dead in unusually public altercations Saturday in Upper Marlboro.

The first homicide appears to have occurred around midnight, when Prince George’s County police received a 911 call about shots fired in the 11800 block of North Marlton Avenue, police spokeswoman Julie Parker said.

Officers arrived to find about 200 people fleeing the party. Police began searching for the source of the gunfire, but the effort proved fruitless as the flood of people dispersed, Parker said.

An hour later, a resident more than a block away called police to report a suspicious person on the front porch. Police arrived to find a 19-year-old man who had been shot and was apparently bleeding for some time. The victim was identified as Rashad Andre Pinkney of Larchmont Avenue in Capitol Heights, who was pronounced dead at a hospital.

Voice-mail messages left on phones registered to the owner of the home where the party occurred were not returned Saturday. Two neighbors said they believed the home was vacant.

The second homicide occurred about nine hours later and four miles away, in the 9600 block of Marlboro Pike. Parker said there were no indications that the homicides were connected.

In that killing, police are investigating what appears to have begun as a robbery, and officers are searching for a person who witnesses say was riding a bike.

The victim, a maintenance worker, was not immediately identified. Parker said a second maintenance worker was shot and was in critical condition at a hospital. Police said the shooter may have been after the workers’ equipment and that they have detained a person of interest.

In connection with the party, police charged a 17-year-old girl who resisted arrest and assaulted a police officer. Parker said the officer suffered a broken leg.