Police: Suspect in 3 shootings turns himself in, police search for motive and weapon

Police are searching for a gun and a motive after Sundance Oliver, the suspect in three shootings and a slew of robberies, turned himself in to police Tuesday. 
Oliver has 12 prior arrests, according to police. 
Police say he is responsible for several crimes throughout the Bronx, Brooklyn and Manhattan. 
Police say Oliver shot a 96-year-old man outside the Kingsborough Houses. The man is in stable condition. 
A few hours later, he shot and killed a 20-year-old man in Manhattan, according to police.  
Early Tuesday morning, police say he shot and killed 17-year-old Keyaira Rattray at the Kingsborough Houses.
Officials say that after he turned himself in on Tuesday morning, he was placed in a holding cell at the precinct and grew violent. They took him to a hospital for an evaluation before returning him to the precinct. 
The NYPD escorted Oliver out of the 77th Precinct on Wednesday. 
“At this point in the investigation, we know both homicide victims are known to our perpetrator,” says “The motive is not yet known at this time as to why he killed them.” 
Oliver is now facing several charges, including murder, attempted murder, robbery and assault.