In November of last year, rookie NYPD cop Peter Liang shot and killed Akai Gurley in the stairwell of the Brooklyn public housing building where he lived. Four months later, a retired correction officer named Willie Groomes shot and killed Gilbert Drogheo on a Brooklyn subway platform. Because Groomes wasn’t indicted for his killing, Liang is arguing in court, he shouldn’t be indicted either.

Liang is using the apparent discrepancy to argue that Brooklyn District Attorney Ken Thompson has an “undeniable bias” against the NYPD, and that Liang’s indictment should be dismissed. DNAinfo’s Murray Weiss reports:

The accusation is contained in a 44-page document filed by Officer Peter Liang’s lawyers that blasted the Brooklyn District Attorney’s office for indicting Liang in the death, which they say was an “accident,” while declining to present evidence to a grand jury when a retired corrections officer shot and killed an unarmed straphanger during a dispute in a downtown Brooklyn subway station last March.

“It is hard — if not impossible — to reconcile the District Attorney’s prosecution for (Liang’s) accidental shooting with the decision of that same office not to prosecute, or even present to a grand jury, the fatal shooting of 32-year-old construction worker Gilbert Drogheo (last March) by retired corrections officer, William Groomes,” the lawyers wrote in a memorandum asking a Brooklyn judge to dismiss Liang’s indictment.

Both Akai Gurley and Gilbert Drogheo were unarmed at the times of their respective deaths. Peter Liang shot Gurley with a bullet that reflected off a wall as Gurley and his girlfriend were walking a stairwell in East New York’s Pink Houses from her apartment to his; Willie Groomes shot Drogheo at point-blank range after pursuing him through the Borough Hall subway station. Liang turned himself in and was charged with second-degree manslaughter and several lesser charges; Groomes was not arrested at the scene of the shooting or charged with a crime.

Liang’s attorneys are correct to point out the glaring differences between the DA’s responses to each slaying—differences for which Thompson should have to answer. But the problem isn’t that Peter Liang was arrested and indicted for killing an unarmed person. It’s that Willie Groomes wasn’t.

Thus far, the DA’s office has been vague about its reasons for declining to bring Groomes’ case to a grand jury. When news of the non-indictment came down last month, it was accompanied by a statement from Thompson alleging that there wasn’t enough evidence to charge Groomes with any crime at all—a statement that stood in stark contrast to witness reports of the shooter drawing his gun while still on the subway and video that showed him following Drogheo through the subway station before killing him. When I published a story about the shooting days after the release of that statement, a spokesperson for Thompson’s office declined to comment on the record.

After that relative silence on the matter, prosecutors revealed at least one facet of their reasoning in a comment on Weiss’ story:

But a spokeman for Thompson, whose mother is a retired NYPD officer, insisted “there is no comparison to the Groomes case, which involved a struggle over a gun — it was a completely different kind of (weapon) discharge. To suggest this case has a similar set of facts is preposterous.”

To my knowledge, this is the first time Thompson’s office has publicly claimed that the Groomes-Drogeho shooting “involved a struggle over a gun,” and it’s unclear where that allegation is coming from. There certainly isn’t any compelling evidence of Drogheo reaching for Groomes’ gun in the video:

[There was a video here]

Peter Liang is in court today, and it’s possible that the judge will accept his request that the charges against him be dropped. In a strange bit of symmetry, a player in the Borough Hall shooting has a court appearance today, too—but it isn’t Groomes. The only person arrested at the scene was Drogheo’s coworker Joscelyn Evering, who allegedly participated in the fight on the subway that preceded the killing, and today he faces charges of assault, harassment, and menacing.

Image via AP. Contact the author at andy@gawker.com.