Duncan Ketter was there by happenstance when he and a female acquaintance climbed into an SUV in East Boston Sunday to complete the sale of 3 ounces of marijuana for $550 in cash, a deal set up by Ketter’s acquaintance, a prosecutor said Tuesday.
“The female happened to be with, by happenstance, Duncan Ketter, who was with her and assisted her in the sale of the marijuana,’’ Suffolk Assistant District Attorney Catherine Ham said in East Boston District Court.
Ketter, the female acquaintance, and the juvenile she made the deal with were in the SUV along with the driver. What Ketter and the female acquaintance did not know, authorities allege, was that Thorus O’Brien was crouched down and hiding in the third seat.
About 4:45 p.m. Sunday, the 18-year-old O’Brien allegedly “popped up” from his hiding place and “pulled out a firearm, cocked the firearm, and pointed it at Duncan Ketter, asking him to hand over the marijuana,” Ham said in court.
When Ketter “verbally resisted,’’ O’Brien allegedly opened fire, shooting the 21-year-old Ketter, killing him where he sat in the SUV, Ham said. The driver of the SUV pulled over, and O’Brien allegedly pushed Ketter’s body out of the car and forced the female to leave the vehicle, Ham said.
Boston police detectives from East Boston and the homicide unit launched an investigation that included studying social media postings, surveillance videos in the area, and law enforcement databases and led to the arrest of the juvenile who allegedly arranged the drug deal that turned into a botched drug rip-off. O’Brien was taken into custody in his Brockton residence Monday.
Ham described the death of Ketter and the arrest to East Boston Municipal Court Judge John E. McDonald Jr. during O’Brien’s arraignment on charges of murder, armed robbery carrying a firearm without a license, and carrying a loaded firearm. A not guilty plea to all charges was entered on O’Brien’s behalf.
Prosecutors said the 16-year-old-old juvenile was arraigned Monday in the Suffolk County Juvenile Court on a charge of delinquency, to wit: armed robbery and armed assault with intent to rob in connection with the incident. His bail was set at $100,000.
Ham told the judge that the juvenile contacted the woman known to him and arranged to purchase a quantity of marijuana Sunday afternoon.
Ham asked the judge to order O’Brien held without bail, noting that O’Brien has had a “glimpse” of criminal process after being found delinquent for carrying a knife and for using a rock as a dangerous weapon.
Defense attorney John P. Morris said he had been appointed to represent O’Brien about an hour before the arraignment took place and could not challenge the government’s summary of the case against his client but might be in a position to do so at a later date.
McDonald ordered O’Brien held without bail and set Jan. 16 as the next hearing date.
Ketter’s relatives who attended the court proceeding left the courthouse without speaking to reporters. Ketter, officials said, had no prior criminal history and was credited with helping save a man who fell onto the Orange Line tracks at North Station in 2014.
A man who identified himself as O’Brien’s stepbrother said he hopes his relative’s involvement with the criminal justice system will soon end.
“I just want him to be free and back out on the streets,” the man said, declining to give his name.John R. Ellement can be reached at firstname.lastname@example.org. Follow him on Twitter @JREbosglobe.