I don't see how it is possible to say that, unless Morse always found a body. Did he?
You do not need a body to prove a murder case because if you hide a body police believe it's murder.
They can also detect residue scents, meaning they can tell if a body has been in a place, even if it’s not there any more.
In October 2013, a jury in Illinois convicted Aurelio Montano, 58, of the first-degree murder of his wife, despite the lack of a body, due in part to evidence provided by cadaver dogs who detected the scent of human remains on a rug.
https://www.theguardian.com/lifeandstyle/2015/sep/08/cadaver-dogs-trained-to-smell-deathMan gets life for murder of wife, who disappeared 24 years ago
A former Aurora resident was sentenced Monday to life in prison for the murder of his wife more than two decades ago in one of the first cases in Illinois where so-called "cadaver dogs" played a key role in obtaining a conviction.
Aurelio Montano, 58, already serving a life term for a drug-related double murder in 1996, was formally sentenced in Kane County court for killing his wife, Maria Guadalupe Montano, who was 35 when she disappeared in July 1990.
http://articles.chicagotribune.com/2014-02-10/news/chi-man-gets-life-for-murder-of-wife-who-disappeared-24-years-ago-20140210_1_aurelio-montano-maria-guadalupe-montano-maribel-barajasOn 23 February 2012, the advocate depute led evidence from a Lothian and Borders Police constable who told the court that they had enlisted the help of specially trained cadaver dogs from South Yorkshire Police to search the offices where David Gilroy and Suzanne Pilley worked. The dogs were specially trained to smell for blood and human remains. The court was told that the dogs, springer spaniels, had identified three areas of interest; one in the basement area of the offices, and two in the boot of David Gilroy's silver Vauxhall Vectra.[14]
David Gilroy, was arrested and charged with her murder. He was found guilty by majority verdict on 15 March 2012 and sentenced to life imprisonment. The judge ordered him to serve a minimum of 18 years in prison. The case is controversial because the prosecution obtained a murder conviction without a body. The body of Suzanne Pilley has never been found.
https://en.wikipedia.org/wiki/Murder_of_Suzanne_PilleyGilroy drove to Lochgilphead for work the day after Ms Pilley went missing, but the journey took around two hours longer than usual. Analysis of fuel consumption suggested that 124 miles of Mr Gilroy's journey were unaccounted. He also collected black bin bags from Lochgilphead.
An examination of Gilroy's car revealed vegetation and soli on the underside, said to be consistent with driving off-road.
Gilroy made 49 calls and sent 400 texts in a month to Ms Pilley. But they stopped on the morning she disappeared suggesting he knew she was dead.
A specialist cadaver dog picked up the scent of a body in the boot of his silver Vauxhall Vectra despite it appearing to have been sprayed with air freshener which Gilroy bought on the lunchtime of the day Ms Pilley went missing.
http://www.heraldscotland.com/news/13414425.Exclusive__Convicted_killer_s_family_reveal_dossier_they_say_proves_innocence_over_Suzanne_Pilley_murder/