As guilty as a louse [closed]
I could not understand this sentence and could not find the meaning. Is it an idiom?
I damn well hope they hang him. I think he’s as guilty as a louse.
The simile "guilty as a louse" doesn't seem to have much currency in English. The only match for it that a Google Books search finds is from Alex Pavesi, The Eighth Detective: A Novel (2020), where it appears twice:
Inspector Wild brought finger and thumb together along the length of his pointed beard and cocked his head back. He let out a long sigh. "I damn well hope it is. I think he's as guilty as a louse."
...
Inspector Wild looked slightly bemused. He gave his friend a wry smile. "What can I say? It seems like you got a lot from that guesswork, but you're exactly right. The wife of the man with the boat saw everything that you've just described. Gordon Foyle is as guilty as a louse. The only thing I don't understand is why he told us about the boat in the first place, if he was guilty the whole time."
Established similes of the form 'guilty as a...' and '...as a louse'
Joseph Clark, Similes, Collected and Arranged (1939) [combined snippets] has only two listings for "guilty as" in common idiomatic usage:
guilty as sin
guilty as a thief
and two listings for "as a louse":
gray as a louse
poor as a louse
To these similes, Bartlett Whiting, Modern Proverbs and Proverbial Sayings (1989) adds two louse-related ones:
As crouse as a new-washed louse
As dead as a louse
Crouse is a Scottish word meaning "Lively; vivacious," according to The American Heritage Dictionary of the English Language, fifth edition (2010).
Henry Bohn, A Hand-book of Proverbs (1888) notes two additional louse similes, both taken from Ray's Proverbs (1672):
As sure as a louse in [one's] bosom
As sure as a louse in Pomfret
Torsten Svartengren, Intensifying Similes in English (1918) has two more:
as proud as a louse
as pert as a louse
Less common similes of the form 'guilty as a'
One-off or little-used instances of "guilty as a" or "as a louse" do pop up in published works from time to time. Most fall into some fairly distinct subcategories. For example, "guilty as a" similes tend to link to children, teenagers, drug users, other criminal, or particular animals:
Children/Teenagers:
guilty as a child [Philippa Gregory, The Lady of the Rivers (2013)]
guilty as a little child found out [Karen McElmurray, Surrendered Child: A Birth Mother's Journey (2011)]
guilty as a small boy caught in an orchard [Leo Bruce, Case with No Conclusion: A Sergeant Beef Mystery (1939)]
guilty as a child caught stealing jam [Betty Rowlands, Over the Edge (2013)]
guilty as a kid caught stealing a candy bar from the corner store [Barbara Curtis, Barbara Hicks, Shari MacDonald & Jane Orcutt, Restoration and Romance (2011)]
guilty as a boy with flour on his hands as the only proof that he had stolen bread [Jim Crace, Quarantine: A Novel (2010)]
guilty as a too-obedient child caught in some unaccustomed mischief [Harriette Arrow, Mountain Path (2012)]
guilty as a kid cutting class Randy Meyers, The Comfort of Lies: A Novel (2013)]
guilty as a fifth grader that just took an extra cookie at a class party [Thomas Bristol, The Adventures of Grace: A Clash of Fortitudes (2011)]
guilty as a schoolgirl caught smoking by the headmistress [Simon Brett, Guns in the Gallery (2012)
guilty as a teenager [Jeffrey Deaver, Garden of Beasts: A Novel of Berlin 1936 (2004)]
guilty as a teenager caught kissing the local bad boy by her mother [Liz Fielding, Her Ideal Husband (2010)]
guilty as a shoplifting teenager [Kristan Higgins, All I Ever Wanted (2014)]
Pets or Other Animals:
guilty as a puppy caught lounging on a sofa [Sharon Oliver, Deliver Me from My Enemies (2012)]
guilty as a dog caught stealing from the master's plate [John Connolly & Jennifer Ridyard, Empire: The Chronicles of the Invaders (2015)]
guilty as a beast of burden [Anosh Irani, The Cripple and His Talismans: A Novel (2005)]
guilty as a fox in a henhouse [Shelley Pearsall, Crooked River (2008)]
guilty as a python swallowing a goat [Richard Sole, A Ritual of the Monkey (2010)]
guilty as a beer bug [Rhonda Gate, Dirty Laundry: Aired Out the Legal Way (2008)]
Adult Mischief/Criminality:
guilty as a dieter with a doughnut [Joan Hess, Poisoned Pins: A Claire Malloy Mystery (2007)]
guilty as a night watchman caught sleeping on the job [Donna Andrews, Murder with Peacocks (2006)]
guilty as a fiend Charles Spurgeon & Harold Chadwick, Morning by Morning (2000)
guilty as a pair of old Nicks [Marie Joseph, Maggie Craig [?] (2012)]
guilty as a pickpocket caught red-handed Carlos Bulosan, All the Conspirators (2005)]
guilty as a pervert in a playground [Linda Davies, Into the Fire (2007)]
guilty as a man who has been caught mixing illegal drugs [Stephen King, Bag of Bones: A Novel (1999)]
guilty as a man with six ounces of Zeus in each pocket [J.D. Robb, Witness in Death (2000)]
guilty as a grave robber [Gayle Greeno, Exile's Return (1995)]
Less common similes of the form 'as a louse'
Similes of the form "as a louse" are not as frequent as similes of the form "as guilty as a" but they make up for their relative rarity with impressive sprightliness:
as brisk as a louse ("Charles Cotton, 'A Voyage to Ireland in Burlesque'" (1670)]
merry as a louse [notes to Louis-Ferdinand Celine, Journey to the End of the Night (translated 1983)]
as flat as a louse [Guy de Maupassant, "The Wreck" (translated 1924)]
as short-lived as a louse [Ramón Pérez de Ayala, The Fox's Paw (translated 1924)]
as ugly as a louse [Jan Giono, The Horseman on the Roof (translated 1953)]
brainless as a louse [Virginia Henley, Insatiable (2004)]
drunk as a louse [Ron Owens, The Real Policeman (2008)
as irritating and provocative as a louse [Ernest Rappaport, Anti-Judaism: A Psychohistory (1975)]
as big as a louse on a flea's arse [Adam Shand, The Skull: Informers, Hit Men and Australia’s Toughest Cop (2010)
as pale as a louse who has been living under a brick [New Statesman (1998) {quoted text not shown in snippet window} (1998)]
as welcome as a louse on a wedding cake [Raymond Chandler, quoted in Victoria Branden, In Defence of Plain English: The Decline and Fall of Literacy in Canada (1992)]
as happy as a louse in a hobo's chest hair [Garry Bushell, Face Down (2014)]
Conclusion
I find no evidence in Google Books or Elephind newspaper database searches that "guilty as a louse" is an established proverbial or idiomatic phrase in English. One character in one book uses it twice, but I can't tell from that record whether the character uses it habitually or whether the author inadvertently trotted out the same turn of phrase through inattentiveness.