All of the outdoors exterior scenes of this episode: "Murder, She Wrote," "The Scent of Murder" (Season 11, Episode 12, that aired January 9, 1995), were filmed on the 127-acre grounds of the Los Angeles County Arboretum and Botanic Garden in Arcadia, CA.
The productions crew used the waterfall at the base of Tallac Knoll, the Old Fashioned Rose Garden, the Celebration Garden, the Herb Garden & the Tropical Greenhouse.
What wasn't used in this episode is the Lagoon and the landmark Queen Anne Cottage (originally built in 1885), which was used in the November 1989 episode, "Night of the Tarantula" with guests Hurd Hatfield, Ji-Tu Cumbuka, John Rhys-Davies & Shani Wallis. The Lagoon & Cottage are best known for their extensive use as Mr. Rourke's (Ricardo Montalban)home on "Fantasy Island" - Rourke's diminutive right-hand man, Tattoo (Hervé Villechaize)filmed his now-iconic, "de plane, de plane!" from the Cottage's bell tower.
Arcadia is just east of Pasadena in the San Gabriel Valley, approx. 20 miles east of Downtown Los Angeles. The Arboretum is directly across the street (Baldwin Ave.) from on of horse racing's finest tracks, Santa Anita.
It should be noted that filming began at the Arboretum in the early 30s when the Lagoon was used for the Johnny Weissmuller-Maureen O'Sullivan "Tarzan" adventures, including "Tarzan Escapes" in 1936.
As it happens, I did public relations/publicity & promotion at the Arboretum in the mid-80s.