Nasir's father, Jermaine Thurman, said he believes his son was in the wrong place at the wrong time.
"I just want everybody to know my son's name. His name is Nasir Marks. He's not just some 18-year-old Black male that was shot. His name is Nasir Marks," Thurman said.
Thurman spoke with Action News at N. 39th and Poplar streets in Mantua on Thursday morning, which is where his son was shot and killed Tuesday.
"He got into no trouble, nothing. All this is way out of left field," Thurman said.
Thurman came to the scene trying to make sense of what happened.
Thurman said the last time they saw their son was when Nasir was practicing his senior speech Tuesday evening.
"Nasir then went see his girlfriend in Mantua, which was about 15 minutes away," said Thurman. "Maybe an hour later, we get a call from Presbyterian Hospital asking are we the parents of Nasir Marks."
It was a call he never expected.
Police said someone shot and killed Nasir just before 7:30 p.m.
"Definitely a tragedy anytime someone is shot and killed in the city. But in this particular evening, we had an 18-year-old and a 15-year-old killed within a half-hour time frame. Clearly two separate shootings," said Philadelphia Chief Inspector Scott Small.
Nasir was supposed to graduate from Overbrook High School in a couple of weeks and then attend Kutztown University in the fall.
His father said Nasir was wearing the university hoodie when he was shot.
"He was the first one that was going to go to college out of my household," Thurman said.
Investigators said according to preliminary reports, the shooter was possibly wearing a ski mask and then got away in a green SUV.
Police are working to collect additional surveillance footage.