The veteran actress Jane Powell, once known for her perky characters in upbeat musicals, takes on a difficult role in a particularly grim episode of “Law & Order: Special Victims Unit” (9 p.m., NBC). During the 1940s and 1950s, Powell performed in such innocent musicals as “Song of the Open Road,” “Holiday in Mexico” and “Nancy Goes to Rio.” Her most-famous film musical was the 1954 classic “Seven Brides for Seven Brothers.”

The indispensable “Film Encyclopedia” by Ephraim Katz (Harper Collins, 1994) describes Powell as “a vivacious blue-eyed blond, (who) typically played sugary, blossoming maidens experiencing innocent first romances, periodically interrupting the plot with a song.” Younger viewers also may recognize Powell, now in her 70s, from her recurring role as Irma on the television comedy “Growing Pains” that ran from 1985 to 1992.

On tonight’s “SVU,” Powell portrays a battered senile woman found wandering the streets in a daze. At first, Benson and Stabler suspect that her son (Jay Thomas, “Cheers,” “Murphy Brown”) may have abused her. Later, they turn their attention to her assisted-care facility where an administrator (Mary Kay Place, “The Big Chill”) recounts the dangers faced by patients and staff, alike.

Barbara Walters revisits one of the milestones of her careers when she returns to Havana to interview Cuban dictator Fidel Castro on “20/20” (9 p.m., ABC). Walters secured a chat with Castro in 1977, shortly after she jumped from NBC to ABC when that network offered her the unheard of salary of $1 million per year.

Tonight, Castro will discuss his feelings about the 1962 Cuban Missile Crisis, which marks its 40th anniversary this month. Castro will also discuss his feelings about Iraq, and his views of current Cuban-American relations.

“Crash Files” (9 p.m., Discovery) examines the doomed voyage of ValuJet Flight 592, which crashed on May 11, 1996, killing all 110 people aboard. Investigators eventually linked the crash to maintenance problems and hazardous cargo, resulting in the FAA’s decision to shut down both the airline and a contractor. Maintenance workers also faced manslaughter charges.

Tonight’s other highlights

Scheduled on “48 Hours Investigates” (7 p.m., CBS): Blood evidence may determine the guilt or innocence of a policeman accused of killing his family, a crime that 11 witnesses swear he did not commit.

The Twins face the Angels in Game 3 of the American League Championship series (7 p.m., Fox).

Michelle Yeoh stars in the 1993 martial arts thriller “Supercop 2” (7 p.m., UPN).

Michael Douglas and Gwyneth Paltrow star in “A Perfect Murder” (7 p.m., TNT), the stylish 1998 remake of “Dial M for Murder.”

Scheduled on “Dateline” (8 p.m., NBC): an interview with attorney Johnnie Cochran, who discusses his controversial role in O.J. Simpson’s legal defense, as well as his new book “A Lawyer’s Life.”

Willie Nelson (as himself) becomes a murder suspect on “Monk” (9 p.m., USA).

Cult choice

A passionate scientist (Sigourney Weaver) becomes obsessed with saving Africa’s endangered primates in the 1988 drama “Gorillas in the Mist” (8 p.m., A&E).

Series notes

Now that she’s engaged, Syd seems surrounded by handsome prospects on “Providence” (7 p.m., NBC) … Tom Bergeron is host of “America’s Funniest Home Videos” (7 p.m., ABC) … Val and Holly spat over their old teddy bear on “What I Like About You” (7:30 p.m., WB).

Sabrina interviews a rap star on “Sabrina, the Teenage Witch” (7:30 p.m., WB).

Mike shelters the wife and daughter of an allegedly abusive cop on “Hack” (8 p.m., CBS).