Tune in Tonight: #CyberSleuths: amateur detectives or TikTok vigilantes?

When does crowd-sourcing become a hysterical cyber-mob? The docuseries “#CyberSleuths: The Idaho Murders” streams on Paramount+. It revisits the gruesome murders of four Idaho college students and the explosion of interest on social media. Self-appointed sleuths pursued leads on TikTok and elsewhere and churned up (or concocted) new leads, theories and “evidence.”

This phenomenon shows how social media and the internet have added a new dimension to an old form of obsession. The O.J. Simpson trial, stemming from a gruesome murder committed 30 years ago, attracted passionate crowds who far outnumbered the throngs of media covering the trial in 1995. While many of these O.J. obsessives harbored theories of their own, they lacked the access to media to make their ideas go viral. The same could probably have been said of the crowds that gathered at the courthouse where the Lindbergh baby murder trial was held in the 1930s. The popularity of “genteel” murder mysteries, from those of Agatha Christie to Louise Penny, probably stems from the same morbid fascination.

#CyberSleuths” takes a skeptical look at this activity, often more akin to hysterical fandom than criminal justice.

— “American Masters” (9 p.m., PBS, r, TV-14, check local listings) presents “How It Means to Be Free,” a joint profile of Black female entertainers Lena Horne, Abbey Lincoln, Nina Simone, Diahann Carroll, Cicely Tyson and Pam Grier, whose presence on the screen and in recording studios helped change society’s attitudes toward race and gender equality, even as they were facing the indignities of the racism and misogyny very much baked into American society.

Seemingly an overnight sensation in 1943, with dazzling appearances in “Cabin in the Sky” and “Stormy Weather,” Horne had all the makings of a major studio star. But both of those films featured all-Black casts. According to the societal norms of the day, any film featuring Horne interacting with white men faced censorship and editing before it could be shown in theaters in many American states. To placate those audiences, Horne’s voice was often dubbed over white actresses’ performances.

Horne would channel her frustration into political activism, and she became the face of progressive groups suing clubs and restaurants that refused entrance to African-Americans. This would result in her being blacklisted in the 1950s as an undesirable left-winger. Eighty years later, the glamorous Horne can seem like just another beautiful face from Hollywood’s Golden Age, but her true story is one of racism, rage and rebellion. In the aftermath of her MGM career, she channeled much of her talent behind the microphone as a recording star.

TONIGHT’S OTHER HIGHLIGHTS

— A doctor suffers a gruesome fate on “FBI” (8 p.m., CBS, r, TV-14).

— “Finding Your Roots With Henry Louis Gates Jr.”(8 p.m., PBS, TV-PG, check local listings) welcomes journalist Sunny Hostin and actor Jesse Williams, who discover hitherto unknown stories about their ancestors.

— A Budapest black market for stolen weapons emerges on “FBI: International” (9 p.m., CBS, r, TV-14).

— Eve’s hiding place proves shocking on “La Brea” (9 p.m., NBC, TV-PG).

— A news anchor is assassinated on “FBI: Most Wanted” (10 p.m., CBS, r, TV-14).

— A family drama draws Ben to Mexico City circa 1953 on “Quantum Leap” (10 p.m., NBC, TV-PG).

CULT CHOICE

A neurotic comedian and television writer (Woody Allen) draws a shy photographer (Diane Keaton) out of her shell and then loses her when she outgrows his didactic and possessive nature in the 1977 comedy “Annie Hall” (8 p.m., TCM, TV-14). Arguably one of the most influential comedies ever made. Its treatment of friends who become lovers and then ex-lovers reinvented conventions of romantic comedy and influenced films like “When Harry Met Sally” and series including “Seinfeld” and its many imitators. But while those successors traded in comedy and even farce, “Annie Hall” was not afraid of its tragic elements. “Annie Hall” was released a month before “Star Wars.” Both films changed entertainment in very different ways.

SERIES NOTES

Fashion Week brings romance on “Night Court” (8 p.m., NBC, TV-PG) … “Name That Tune” (8 p.m., Fox, TV-PG) … “Celebrity Wheel of Fortune” (8 p.m., ABC, r, TV-PG) … Trey takes charge on “Extended Family” (8:30 p.m., NBC, TV-PG).

Rob Lowe hosts “The Floor” (9 p.m., Fox, TV-PG) … An officer vanishes on “Will Trent” (9 p.m., ABC, r, TV-14) … Kidnappings form a pattern on “The Rookie” (10 p.m., ABC, r, TV-14).

LATE NIGHT

Jimmy Fallon welcomes Tracee Ellis Ross, Rod Stewart and Jools Holland on “The Tonight Show” (11:35 p.m., NBC) … Molly Ringwald and Nana Kwame Adjei-Brenyah visit “Late Night With Seth Meyers” (12:35 a.m., NBC) … Taylor Tomlinson hosts “After Midnight” (12:35 a.m., CBS).