A fired-up police Commissioner William G. Gross ripped into ACLU “paper warriors” for suing the city over a gang database, saying the civil rights advocates are turning a blind eye to “atrocities.”

“No ACLU present when we have to explain to a mother that her son or daughter was horribly murdered by gang violence,” Gross wrote in a scathing private Facebook post obtained by the Herald.

“No ACLU when officers are shot. No ACLU when we help citizens,” he added. “Despite the paper warriors, we’ll continue to do our jobs.”

READ MORE: The ACLU responds to Boston Police Commissioner William G. Gross

Gross was lashing back at the local chapter of the American Civil Liberties Union for being part of a public records lawsuit claiming Boston police are too secretive about how they monitor suspected gang members.

That system, the ACLU claims, targets, labels and investigates a disproportionate amount of black and brown students who may not belong to a gang.

Police spokesman Sgt. John Boyle said last night the commissioner “shared his opinion on his personal Facebook page.” He declined to comment further.

That post included Gross calling out the ACLU on a number of fronts — especially about the ruthless MS-13 gang.

“I sure as hell didn’t see the ACLU in El Salvador working to find a solution to our youth being inducted into the MS-13 gang …,” he wrote, saying he did travel to MS-13’s homeland and “took a hell of a risk while doing so.”

MS-13 has been wreaking havoc in Boston with violent killings in Eastie, robberies, extortion, drug dealing and racketeering — with 49 gang members recently convicted, many of them facing life in prison.

Gross said he “didn’t see” the ACLU back police or 22 youth programs working together to curb the gang’s “atrocities.”

Gross also knocked the lawyers’ group for not having the “common decency” to call with condolences after a city cop was shot in the face.

Officer John Moynihan was shot point-blank in the cheek by a convicted felon in March 2015 during a traffic stop in Roxbury. After remaining in critical condition, Moynihan made a miraculous recovery. The felon was killed that day by other officers.

“I sure as hell saw a member of the ACLU in the background taking pictures as a certain group tried to crash through the crime scene three hours later,” Gross said of that day.

“No ACLU when officers are shot. No ACLU when we help,” he added in his post. “But always hiding and waiting for a slow news day to justify their existence.”

The lawsuit seeks records providing the demographics of the youths in their gang systems. The ACLU asked for the records in May and had not received “adequate response,” they claim.

The ACLU did not respond to Herald requests for comment last night on the police commissioner’s harsh criticism.

ACLU of Massachusetts, the Children’s Law Center of Massachusetts, Greater Boston Legal Services, the Justice Center of Southeast Massachusetts, the Muslim Justice League, the National Lawyers Guild, Massachusetts Chapter, and the Political Asylum/Immigration Representation Project are all involved in the lawsuit.

Alexi Cohan contributed to this report.