The girlfriend of slain New York City activist Ryan Carson was unable to pick her boyfriend’s suspected killer from a photo lineup — and that could potentially hurt the case, according to legal experts.

Carson’s partner, who was with him the night he was fatally stabbed this month, was not able to pick suspect Brian Dowling, 18, from a photo array and instead picked a different person, Brooklyn prosecutors said during Dowling’s arraignment Thursday.

The girlfriend remains traumatized by the slaying and has trouble remembering basic details about the incident, a police official told ABC 7 Friday.  

Two witnesses positively identified Dowling as Carson’s killer from a photo lineup and said he was the person seen stabbing the activist in a video of the senseless attack, prosecutors did note.

Former Manhattan prosecutor turned defense lawyer Mark Bederow told the Messenger it was “potentially devastating and crippling” that the girlfriend could not identify Dowling.

But Bederow, who is not involved in the case, also said that it “doesn’t by any means mean that it’s over.”

“It’s really too early to tell,” he told the outlet, pointing out other evidence could make up for that photo array miss.

“If they found a weapon at this guy’s apartment and it has the DNA of the victim, that’s compelling in the other direction,” he said.

Ex-Brooklyn prosecutor Julie Rendelman told the Messenger the girlfriend’s trouble identifying Dowling is something the defense could potentially raise as reasonable doubt.

But she also pointed out “the stabbing is caught on video and the defendant’s face is fairly clear.”

“It will likely be argued by the prosecution that the witness’ trauma in watching her boyfriend be stabbed before her eyes impacted her ability to identify the defendant,” the now-defense lawyer said.

Carson and his girlfriend were heading home from a wedding on Long Island when the stabbing happened, police said.

The assailant seemed to target Carson at random, forcing the beloved community advocate to stand between the stranger and his girlfriend, according to surveillance footage obtained by The Post showed.

The unhinged man can be heard yelling “I’ll kill you!” before the two scuffle, with Carson eventually tumbling over the bus stop bench while the attacker pulls out a knife and stabs him three times, according to cops and the video.

Kenneth Jamal Montgomery, Dowling’s defense lawyer, agreed the photo array issue could help his client, but said to the Messenger “I am waiting to review the discovery and all of its context.”

Dowling is facing a second-degree murder charge.