actually, if you timed it right in la you could watch mike Douglas, Merv Griffith, and dick Cavett on the indie stations in la in the 80s from 1 to 4 there were slight differences cavett tried to be more current event-oriented Douglas tried to be Carson and Merv just liked hanging out with famous people
And someone mentioned Monk and poison. The two Monk episodes with someone murdered on the stage are:
The first episode: Someone was shot on stage at a political rally.
Mr. Monk goes to the Theater. An actor in a play was stabbed. A tainted apple was a factor.
Cavett also had on older actors who were no longer working, so it wasn’t just celebrities whoring out their latest project. I preferred Cavett to any of the others, although he’d always get a little weird with attractive women guests…like a blushing schoolboy.
Mark Sandman, lead singer for the band Morphine, died of a heart attack on stage in the middle of a performance.
Likewise, Dick Shawn. When a stagehand asked if there was a doctor present, the audience thought it was part of his act. They only started to leave the theater after the paramedics arrived.
A tenor died onstage at the Metropolitan Opera in 1996, seconds after singing the words “Too bad you can only live so long.”
British comedian/ magician Tommy Cooper collapsed and died onstage during a live TV broadcast.
British comedian Eric Morecambe collapsed onstage while taking a curtain call. e died in hospital a short time later.
Dimebag Darrell was shot to death on stage.
Irene Ryan, aka “Granny” on The Beverly Hillbillies, also dropped dead on stage while acting in a play not long after the TV show was cancelled.
Albert Brooks’ father, Harry Einstein (aka Parkyakarkus) died on stage in 1958 during a roast for Lucille Ball and Desi Arnaz.
Indonesian singer Irma Bule was performing on stage with a cobra, which bit her. She died 45 minutes later.
Yet another - Country Dick Montana of The Beat Farmers dropped dead while performing on stage.
His songs were covered by and co-written with Emmylou Harris, Steve Earle, Linda Ronstadt, Steve Young, Del McCoury, and Laurie Lewis, among many others.
Olney died of an apparent heart attack during a performance onstage at the 30A Songwriter Festival in Santa Rosa Beach, Florida, on January 18, 2020, at the age of seventy-one.[6][8][15] He was in the middle of his third song when he stopped, apologized and shut his eyes, according to fellow musician Scott Miller, who was accompanying Olney.
The Ronstadt/Harris version of 1917 is a gutpunch.
Close, but not quite
“not long after” was still a couple of years. She originated the role of Berthe in Pippin (in which her signature song includes, ironically, the lines “it’s time to start livin’, time to take a little from this world we’re given”) in 1972 (Hillbillies was cancelled in 1971) and was still performing the part when she was stricken on stage.
The big laugh line from that song, though, was “It’s hard to believe I’m being led astray by a man who calls me ‘Granny!’”
Better she shoulda doctored hersself, ‘steada goin’ t’see them California quacks! 
I’m pretty sure Rapping Grannies or Old White Guys who Talk Black weren’t as common in the 90s as pop culture lead us to believe.
OK; lots of people have died onstage, but was any one of them declared a homicide? Let alone one by a person or persons unknown, so there was an investigation by detectives?
It seems that the essence of what we were originally talking about that frequently happens on TV, is an onstage/camera murder, not merely a death.
Season 3 of Only Murders in the Building features a death onstage, we just learned from the last ep of season 2.
As noted upthread, Dimebag Darrell from the bands Pantera and Damageplan was shot and killed onstage.